<PAGE>
 
                                  FORM 10-Q/A
                                AMENDMENT NO. 1

                      SECURITIES AND EXCHANGE COMMISSION
                            WASHINGTON, D.C. 20549
                                        
(MARK ONE)
   [X]  QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15 (D) OF THE SECURITIES
        EXCHANGE ACT OF 1934.
                For the quarterly period ended  March 31, 1998.
                                      OR
   [_]  TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(D) OF THE SECURITIES
        EXCHANGE ACT OF 1934

For the transition period from _____ to _____

                        Commission file number 0-27750
                                               -------
                                  IMPATH INC.
                   ---------------------------------------- 
            (exact name of registrant as specified in its charter)

<TABLE> 
  <S>                                <C>                              <C> 
            DELAWARE                             8071                     13-3459685
  (State or other jurisdiction of    (Primary Standard Industrial      (I.R.S. Employer
   incorporation or organization)     Classification Code Number)     Identification No.)
</TABLE>

                        521 West 57th Street, 6th Floor
                           NEW YORK, NEW YORK 10019
                                (212) 698-0300
              (Address, including zip code, and telephone number,
                   ----------------------------------------
       including area code, of registrant's principal executive offices)



Indicate by check mark whether the registrant (1) has filed all reports required
to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during
the preceding 12 months (or for such shorter period that the registrant was
required to file such reports), and (2) has been subject to such filing
requirements for the past 90 days.


Yes    X    No   ___
    -------         

     Indicate the number of shares outstanding of each of the issuer's classes
of common stock, as of the latest practicable date.


CLASS                                        OUTSTANDING AT MARCH 31, 1998
-----                                        -----------------------------
Common Stock, par value                                7,825,685
$ .005 per share

                                       1
<PAGE>
 
The registrant hereby amends its Quarterly Report on Form 10-Q for the quarter
ended March 31, 1998 to correct errors in the Consolidated Statements of Cash
Flows (Unaudited) included in the Financial Statements at Item 1 and to correct
a typographical error in the first sentence of the fourth paragraph (105%
instead of 10.5%) of Management's Discussion and Analysis included at Item 2.
Although the only change to the Financial Statements included in Item 1 is to
the Consolidated Statements of Cash Flows (Unaudited), the Financial Statements
are set forth in full in this Form 10-Q/A pursuant to Regulation Section
240.12b-15.

<TABLE> 
<CAPTION> 
                                                                         PAGE NUMBER
                                                                         -----------
<S>                                                                      <C> 
Item 1.  Consolidated Financial Statements (Unaudited):

  
        Consolidated Balance Sheets at March 31, 1998
        and December 31, 1997................................................... 3
 
        Consolidated Statements of Operations for the Three
        Months Ended March 31, 1998 and March 31, 1997.......................... 4
 
        Consolidated Statement of Stockholders' Equity for the
        Three Months Ended March 31, 1998....................................... 5
 
        Consolidated Statements of Cash Flows for the Three
        Months Ended March 31, 1998 and March 31, 1997.......................... 6
 
  
        Notes to Consolidated Financial Statements.............................. 7
 
Item 2. Management's Discussion and Analysis
of Financial Condition and Results of Operations................................ 8
 
Signatures...................................................................... 10
</TABLE>

                                       2
<PAGE>
 
            Item 1.  Consolidated Financial Statements (Unaudited)


                         IMPATH INC. AND SUBSIDIARIES

                          Consolidated Balance Sheets

<TABLE>
<CAPTION>
                                                                 MARCH 31,        DEC. 31, 
                                                                   1998             1997  
                            ASSETS                              (UNAUDITED)      (AUDITED)
                                                               -------------    ----------
<S>                                                            <C>             <C>
Current assets:
 Cash and cash equivalents                                      $ 66,208,440   $   325,285
 Marketable securities at market value                            17,660,007    13,952,148
 Accounts receivable, net of allowance for doubtful accounts      13,759,593    11,948,229
 Prepaid expenses                                                    423,240       276,073
 Deferred tax assets, net                                             53,427        53,427
 Other current assets                                                769,251       703,753
                                                                ------------   -----------
 Total current assets                                             98,873,958    27,258,915
 
Fixed assets, less accumulated depreciation and amortization      12,390,773    10,475,575
Deposits and other assets                                            180,034       334,167
Intangible assets, net of accumulated amortization                 8,157,531     8,273,636
                                                                ------------   -----------
 Total assets                                                   $119,602,296   $46,342,293
                                                                ============   ===========
 
               LIABILITIES AND STOCKHOLDERS' EQUITY
 
Current liabilities:
 Current portion of capital lease obligations                   $  1,321,439   $ 1,222,281
 Current portion of note payable                                     829,333       700,000
 Accounts payable                                                  2,191,362       956,648
 Construction payments payable                                             -     1,542,199
 Income taxes payable                                                693,078       158,094
 Accrued expenses                                                    935,058       728,353
                                                                ------------   -----------
  Total current liabilities                                        5,970,270     5,307,575
                                                                ------------   -----------
Capital lease obligations, net of current portion                  2,027,623     2,451,587
Note payable, net of current portion                                 189,667       274,000
                                                                                          
Stockholders' equity:                                                                     
 Common stock                                                         39,164        27,294
 Additional paid-in capital                                      105,752,313    33,893,774 
 Retained earnings                                                 6,226,228     5,148,077    
 Unrealized net depreciation of marketable securities                (37,569)      (83,881)   
                                                                ------------   -----------    
                                                                 111,980,136    38,985,264    
                                                                                              
Less:                                                                                         
 Cost of 7,088 shares of common stock held in treasury                  (100)         (100)   
 Deferred compensation                                              (565,300)     (676,033)   
                                                                ------------   -----------    
 Total stockholders' equity                                      111,414,736    38,309,131    
                                                                ------------   -----------    
 Total liabilities and stockholders' equity                     $119,602,296   $46,342,293    
                                                                ============   ===========    
</TABLE>

See accompanying notes to consolidated financial statements.

                                       3
<PAGE>
 
                         IMPATH INC. AND SUBSIDIARIES

                     Consolidated Statements of Operations
                                  (Unaudited)

<TABLE>
<CAPTION>
                                                           THREE MONTHS ENDED MARCH 31,
                                                         --------------------------------
                                                                 1998            1997 
                                                                ------          ------ 
<S>                                                          <C>             <C> 
Revenues:
 Net diagnostic and prognostic services                      $11,603,161     $7,824,950
 Contract laboratory services                                    109,347         20,036
                                                             -----------     ----------
  Total revenues                                              11,712,508      7,844,986
                                                             -----------     ----------
Operating expenses:
 Salaries and related costs                                    4,729,622      3,238,196
 Selling, general and administrative                           5,282,104      3,775,987
                                                             -----------     ----------
  Total operating expenses                                    10,011,726      7,014,183
                                                             -----------     ----------
    Income from operations                                     1,700,782        830,803
 
Interest income                                                  341,138         62,644
Interest expense                                                 133,109         81,418
Gains on marketable securities, net                                    -        202,537
                                                             -----------     ----------
 
    Income before income tax expense                           1,908,811      1,014,566
 
Income tax expense                                              (830,660)      (451,089)
                                                             -----------     ----------
Net income available to common stockholders                  $ 1,078,151     $  563,477
                                                             ===========     ==========
 
Per common and common equivalent share:
Basic:
 Net income per common share                                        $.18           $.11
                                                             ===========     ==========
 Weighted average common and common
   Equivalent shares outstanding                               6,011,000      5,352,000
                                                             ===========     ==========
Dilutive:
 
 Net income per common share-assuming dilution                      $.17           $.10
                                                             ===========     ==========
 Weighted average common and common
   Equivalent shares outstanding-assuming dilution             6,460,000      5,754,000
                                                             ===========     ==========
</TABLE>

                                       4
<PAGE>
 
                         IMPATH INC. AND SUBSIDIARIES

                Consolidated Statement of Stockholders' Equity
                       Three Months ended March 31, 1998
                                  (Unaudited)

<TABLE>
<CAPTION>
                                         COMMON STOCK         Additional                         UNREALIZED NET       
                                         ------------                                                                 
                                                                PAID-IN         ACCUMULATED     DEPRECIATION OF       
                                      Shares      Amount        CAPITAL           EARNINGS         SECURITIES          
                                      ------      ------       ---------        -----------     ---------------
<S>                                   <C>         <C>         <C>               <C>             <C>      
Balance at December 31, 1997          5,458,827   $27,294     $ 33,893,774       $5,148,077         ($83,881)       
                                      =========   =======     ============       ==========         ========        
Common shares issued upon                                                                                           
     exercise of stock options           44,615       223           91,069                                           
Common shares issued upon                                                                                           
     exercise of warrants                29,331       147          102,659                                          
Common shares issued upon                                                                                           
     secondary offering, net          2,300,000    11,500       71,704,811                                          
Compensation associated with                                                                                        
     issuance of options to non-                                                                                    
     employees                                                                                                      
Amortization of deferred                                                                                            
     compensation                                                  (40,000)                                         
Change in unrealized net                                                                                            
     depreciation of securities                                                                       46,312        
Net income for the period                                                                                           
     ended March 31, 1998                                                         1,078,151                         
                                      ---------   -------     ------------       ----------         -------- 
Balance at March 31, 1998             7,832,773   $39,164     $105,752,313       $6,226,228         ($37,569)       
                                      =========   =======     ============       ==========         ========         
<CAPTION> 
                                                    TREASURY        DEFERRED      
                                                      STOCK       COMPENSATION       TOTAL 
                                                  ------------   --------------    ---------
<S>                                               <C>            <C>              <C> 
Balance at December 31, 1997                          ($100)       ($676,033)     $ 38,309,131    
                                                      =====        =========      ============    
Common shares issued upon                                                                         
     exercise of stock options                                                          91,292
Common shares issued upon                                                                         
     exercise of warrants                                                              102,806
Common shares issued upon                                                                         
     secondary offering, net                                                        71,716,311
Compensation associated with                                                                      
     issuance of options to non-                                                                  
     employees                                                                                    
Amortization of deferred                                              40,500            40,500                  
     compensation                                                     70,233            30,233
Change in unrealized net                                                                          
     depreciation of securities                                                         46,312
Net income for the period                                                                         
     ended March 31, 1998                                                            1,078,151
                                                      -----        ---------      ------------
Balance at March 31, 1998                             ($100)       ($565,300)     $111,414,736
                                                      =====        =========      ============
</TABLE>

See accompanying notes to consolidated financial statements.
                                       
                                       5
<PAGE>
 
                         IMPATH INC. AND SUBSIDIARIES
                                        
                     Consolidated Statements of Cash Flows
                                  (Unaudited)

<TABLE> 
<CAPTION> 
                                                                           THREE MONTHS ENDED MARCH 31,
                                                                           ----------------------------
                                                                                 1998          1997
                                                                                ------        ------
<S>                                                                          <C>           <C>
Cash flows from operating activities:
   Net income                                                                $ 1,078,151   $   563,477
    Adjustments to reconcile net income to net cash provided by (used in)
    operating activities:
    Depreciation and amortization                                                553,457       349,239
    Provision for uncollectible accounts receivable                            1,163,396     1,100,349
    Non-cash compensation                                                         70,733        31,896
         Changes in assets and liabilities:
         (Increase) in accounts receivable                                    (2,974,760)   (2,688,028)
         (Increase) in prepaid expenses and current assets                      (212,665)     (109,296)
         Decrease (increase) in deposits and other assets                        154,133       (12,390)
         (Decrease) in accounts payable and accrued expenses                    (100,780)     (444,180)
         Increase (decrease) in income taxes payable                             534,984      (147,911)
                                                                             -----------   -----------
       Total adjustments                                                        (811,502)   (1,920,321)
                                                                             -----------   -----------
Net cash provided by (used in) operating activities                              266,649    (1,356,844)
                                                                             -----------   -----------
Cash flows from investing activities:
    Purchases of marketable securities                                        (7,273,339)    3,745,669
    Sales/maturities of marketable securities                                  3,611,792             -
   Acquisitions of businesses                                                          -    (1,175,000)
   Capital expenditures                                                       (2,307,550)     (145,279)
                                                                             -----------   -----------
Net cash (used in) provided by investing activities                           (5,969,097)    2,425,390
                                                                             -----------   -----------
Cash flows from financing activities:
  Issuance of common stock                                                       194,098       113,006
  Proceeds of secondary offering, net of registration costs to date           71,716,311             -
  Payments of capital lease obligations                                         (324,806)     (212,991)
  Payments received on officer loans                                                   -           521
                                                                             -----------   -----------
Net cash provided by (used in) financing activities                           71,585,603       (99,464)
                                                                             -----------   -----------
Net increase in cash and cash equivalents                                     65,883,155       969,082
Cash and cash equivalents at beginning of period                                 325,285       941,903
                                                                             -----------   -----------
Cash and cash equivalents at end of period                                   $66,208,440   $ 1,910,985
                                                                             ===========   ===========
</TABLE>

See accompanying notes to consolidated financial statements.
                                       
                                       6
<PAGE>
 
                                  IMPATH INC.
                                        
                  Notes to Consolidated Financial Statements
                                  (unaudited)

GENERAL:

The accompanying unaudited consolidated financial statements have been prepared
by management in accordance with the rules and regulations of the United States
Securities and Exchange Commission.

In the opinion of IMPATH Inc. (the "Company" or "IMPATH"), the accompanying
unaudited consolidated financial statements contain all adjustments, consisting
only of normal recurring adjustments necessary for the fair presentation of the
financial information for all periods presented. Results for the interim periods
are not necessarily indicative of the results for an entire year and do not
include all of the information and footnotes required by generally accepted
accounting principles for complete financial statements. These consolidated
financial statements should be read in conjunction with the consolidated
financial statements and the notes thereto contained in the Company's Annual
Report on Form 10-K for the year ended December 31, 1997.

NET INCOME PER SHARE:

Net income per share, basic is based on the weighted average number of shares of
common stock outstanding.  Fully diluted earnings per share is based on the
weighted average number of shares of common stock and common equivalent shares
outstanding.  Common equivalent shares from stock options and warrants are
included in the computation using the treasury stock method to the extent their
effect is dilutive.

Comprehensive net income is equal to the net income reported adjusted for the
unrealized net appreciation of marketable securities, net of related deferred
taxes.  Comprehensive net income for the three months ended March 31, 1998 and
1997 was $1,124,463 and $563,477, respectively.

INVESTMENT:

In accordance with Statement of Financial Accounting Standards ("SFAS") No. 115,
the Company's investments (consisting primarily of government and corporate
fixed income securities) were classified as available for sale.  As a result,
the unrealized depreciation is recorded as a separate component of stockholder's
equity, net of related deferred taxes.  Prior to October 1, 1997, the Company's
investments were classified as trading securities with unrealized gains and
losses reported in the consolidated statement of operations.  The Company
currently has approximately $83,000,000 invested in a portfolio of short term
fixed income securities , approximately $70,000,000 of which was generated from
the net proceeds of an underwritten public offering of 2,300,000 shares of
common stock in March 1998.  At March 31, 1998, approximately $66,000,000 of
securities with original maturities of  three month or less were included as
cash equivalents.  The remaining securities included in the investment portfolio
with original maturities that exceed three months are included in current
assets.

                                       7
<PAGE>
 
                 ITEM 2.  MANAGEMENT'S DISCUSSION AND ANALYSIS
               OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS
                                        

                       THREE MONTHS ENDED MARCH 31, 1998
                COMPARED WITH THREE MONTHS ENDED MARCH 31, 1997

The Company's total revenues for the first three months of 1998 and 1997 were
$11,713,000 and $7,845,000, respectively, representing an increase of
$3,868,000, or 49.3%, in 1998.  This growth was primarily attributable to a
53.6% increase in case volume resulting from increased sales and marketing
activities and to the successful integration of the Company's 1997 acquisitions
of certain assets of Oncogenetics, Inc., Immunodiagnostic Laboratories, Inc.,
the Gencare division of BioReference Laboratories, Inc. and Aeron Biotechnology,
Inc.  In addition, revenue realization per case increased due to product mix
changes toward cases which carry higher reimbursement rates and to payor mix
shifts away from direct hospital billing towards private insurance.

Salaries and related costs for the first three months of 1998 and 1997 were
$4,730,000 and $3,238,000, respectively, representing an increase of $1,492,000,
or 46.1%, in 1998.  This increase was the result of increased personnel
headcount due to the increase in case volume, as well as personnel costs
incurred in connection  with the Company's expansion.  Salaries and related
costs, as a percentage of total revenues decreased to 40.4% in 1998 from 41.3%
in 1997.

Selling, general and administrative expenses for the first three months of 1998
and 1997 were $5,282,000 and $3,776,000, respectively, representing an increase
of $1,506,000, or 39.9%, in 1998. The largest component of this increase was
$502,000 in incremental courier and laboratory supply costs due to rapid case
volume growth.  The Company also incurred an additional $204,000 in amortization
and depreciation expenses associated with the Company's asset acquisitions and
capital equipment requirements. In addition, the Company incurred $156,000 in
incremental travel related expenses and professional fees associated with
expanded sales, marketing and investor relations activities.  Selling, general
and administrative expenses as a percentage of total revenues decreased to 45.1%
in 1998 from 48.1% in 1997.

Income from operations for the first three months of 1998 and 1997 was
$1,701,000 and $831,000, respectively, representing an increase of $870,000, or
105%, in 1998.  The 1998 figure reflects increased company operating margins
from its core diagnostic and prognostic services and the Company's continued
expansion of its oncology business, particularly in molecular and Cytogenetics
testing for cancer.  As a percentage of total revenues, income from operations
increased to 14.5% in 1998 from 10.6% in 1997.

Other income, net for the first three months of 1998 and 1997 was $208,000 and
$184,000, respectively, representing an increase of $24,000 in 1998. The
increase was the result of increased interest income generated from the proceeds
of the Company's secondary public offering of common stock in March 1998,
partially offset by increased interest expense due to additional capital lease
obligations.

The tax provision for the first three months of 1998 of approximately $831,000
reflects federal, state and local income tax expense.  The Company has estimated
its annual effective tax rate for 1998 to be approximately 44% which is in line
with the current provision.

Net income for the first three months of 1998 and 1997 was $1,078,000 and
$563,000, respectively, representing an increase of $515,000, or 91.5% in 1998.
As a percentage of total revenues, net income increased to 9.2% in 1998 from
7.2% in 1997, which was due to the factors described above.

                                       8
<PAGE>
 
LIQUIDITY AND CAPITAL RESOURCES

Since inception, the Company has financed its operations through its February
1996 initial public offering, the private issuance of convertible preferred
stock, secured term loans and operating and capital equipment leases.  In March
1998, the Company raised approximately $72,000,000 of capital through an
underwritten secondary public offering of Common Stock.  The proceeds will be
used to fund the Company's growth strategy and the continued development of its
outcomes database.

The Company's cash and cash equivalent balances at March 31, 1998 and December
31, 1997 were $66,208,000 and $325,000, respectively, representing an increase
of $65,883,000 in 1998, primarily due to the net cash proceeds generated from
the secondary public offering of 2.3 million shares of common stock.  The
Company has invested approximately $70,000,000 of the proceeds in a portfolio of
short-term government and corporate fixed income securities.

For the quarter ended March 31, 1998, net cash provided by operating activities
was approximately $266,000.  This resulted from higher net income, as well as an
increase in income taxes payable of $535,000 due to timing differences between
book and taxable income, offset by an increase in accounts receivable net of
allowance for bad debt of approximately $1,811,000 due to rapid sales growth.
The Company also reduced its accounts payable and accrued expenses by
approximately $100,000.

For the quarter ending March 31, 1998, the Company invested approximately
$3,600,000 of the proceeds from the secondary offering in marketable securities
and incurred approximately  $2,300,000 in capital expenditures, including costs
associated with the Company's relocation of its New York facilities.

The Company received approximately $194,000 for the quarter ended March 31, 1998
through the issuance of Common Stock upon the exercise of incentive stock
options and warrants.  The Company used approximately $325,000 to satisfy its
capital lease obligations.

In March 1998, the Company established an unsecured line of credit at an
aggregate amount of  $10.0 million with Fleet Bank.  Borrowing under the line
will bear interest at LIBOR plus 2.25%.  As of March 31, 1998, the Company had
not drawn on the line of credit.

The Company's growth strategy is anticipated to be financed through the net
proceeds from the secondary public offering of 2,300,000 shares of its Common
Stock, its current cash resources and existing third-party credit facilities.
The Company believes the combination of these sources will be sufficient to fund
its operations and satisfy the Company's cash requirements for the next 12
months and the foreseeable future.  There may be circumstances, however, that
would accelerate the Company's use of proceeds from the secondary public
offering.  If this occurs, the Company may, from time to time, incur additional
indebtedness or issue, in public or private transactions, equity or debt
securities.  However, there can be no assurance that suitable debt or equity
financing will be available to the Company.

IMPACT OF INFLATION AND CHANGING PRICES

The impact of inflation and changing prices on the Company has been primarily
limited to salary, laboratory and operating supplies and rent increases and has
not been material to date to the Company's operations.  In the future, the
Company may not be able to raise the prices for its cases by an amount
sufficient to cover the cost of inflation, although the Company is responding to
these concerns by attempting to increase the volume and adjust the product mix
of its business.

                                       9
<PAGE>
 
                                  SIGNATURES


Pursuant to the requirements of the Securities Exchange Act of 1934, the
registrant has duly caused this report to be signed on its behalf by the
undersigned thereunto duly authorized.


     Dated: May 14, 1998                     IMPATH INC.                 
                                             -----------                 
                                             (Registrant)                
                                                                         
                                                                         
     Dated: May 14, 1998                     By /s/ ANU D. SAAD     
                                             ---------------------------- 
                                             Anu D. Saad, Ph.D.          
                                             President and Chief         
                                             Executive Officer           
                                                                         
                                                                         
     Dated: May 14, 1998                     By /s/ JOHN P. GANDOLFO   
                                             ----------------------------
                                             John P. Gandolfo            
                                             Executive Vice President,   
                                             Chief Financial Officer     
                                             and Principal Accounting    
                                             Officer                      

                                       10