mucinous carcinoma ( mc ) of the breast is not a common disease and the incidence of mc was reported to range from 1% to 6% of all primary breast cancers ( 1 - 4 ) . mc of the breast was characterized by a large amount of mucin production and in general , defined as having a mucinous component of 50% or more ( 5 , 6 ) . those lesions had different features from invasive ductal carcinoma - not otherwise specified ( idc - nos ) . median age at diagnosis was older than 60 and older than that of idc - nos ( 4 , 6 ) . furthermore , mc showed more favorable clinicopathological characteristics , such as lower incidence of nodal metastasis , higher expression of estrogen and progesterone receptors , and differentiated grade ( 2 , 6 , 7 ) . therefore , prognosis of mc is better than that of idc - nos with 10-yr survival rates better than 80% ( 1 , 8) . histologically mc is classified into 2 subgroups based on the degree of cellularity , which are pure type and mixed mucinous - ductal type ( 9 ) . however , cut - off values of the mucinous component for defining pure type mc was not standardized , and later , others divided mc into type a and type b ( 10 ) . the former is the classical type with large amounts of mucins and the latter is a variant type with neuroendocrine differentiation or feature of signet ring cells ( 5 , 10 ) . prognostic significance of clinicopathological characteristics in mc patients is not well established , because of its low incidence rate and lack of a standard definition . treatment guidelines for mc are mostly extrapolated from data based on invasive ductal carcinoma ( idc ) without clear validation . as incidence of breast cancer was significantly increasing in korea ( 11 , 12 ) , it was necessary to investigate incidence rates , clinicopathological characteristics , and prognosis of mc to prepare an adequate treatment guideline . but there are few studies on mc and information is limited . in this study , we investigated the clinicopathological characteristics and treatment patterns for mc and compared survivals of mc with those of idc - nos . we retrospectively reviewed the data of 4,932 breast cancer patients who were treated at the department of surgery , yonsei university college of medicine in seoul , korea between january 1986 and december 2006 . these patients were compared with 3,936 patients with idc - nos who were treated during the same period . however , slides of the remaining 30 patients were not available and we reviewed these cases through previous pathologic reports . pure type mc was defined as having a mucinous component of more than 90% and specialized pathologists with extensive experience in breast pathology performed a pathologic slide review . sixty - one ( 82.4% ) of 74 patients were categorized as having pure type mc . data regarding patient demographics , histopathology of primary tumor , treatment patterns , and survivals were obtained by reviewing medical records . patients were treated with either mastectomy or lumpectomy and axillary lymph node dissection or sentinel lymph node biopsy with local radiotherapy . after completion of surgery , adjuvant treatments were administered as indicated based on international guidelines . tumor stage was based on the 6th american joint committee on cancer ( ajcc ) criteria . ten percent or more of positively stained cells was used as the cut - off for estrogen receptor ( er ) and progesterone receptor ( pr ) positivity . her-2/neu staining was scored from 0 to 3 + according to the guideline suggested for herceptest ( dako , glostrup , denmark ) ( 13 ) . her-2/neu immunohistochemical staining was considered positive when strong ( 3 + ) membranous staining was observed , whereas cases with 0 to 1 + were regarded as negative . because fluorescent in - situ hybridization test had not been performed routinely , cases with equivocal ( 2 + ) staining were excluded in statistical analyses . clinical follow - up included history taking , physical examination , laboratory tests and radiologic imaging every 6 - 12 months . survival curves were determined and plotted using the kaplan - meier method and group differences in survival time were investigated by log - rank test . median age at diagnosis was 47 yr in all patients ( range , 20 - 93 yr ) , and age at diagnosis was much younger in mc patients than in idc - nos patients with statistical significance ( p=0.022 ) ; 45 yr old for mc patients and 47 yr old for idc - nos patients . among 74 patients whose slides were available for reviewing , 61 patients ( 82.4% ) were pure mc and 13 ( 17.6% ) were mixed mucinous - ductal carcinoma . mammographic and sonographic findings according to breast imaging reporting and data system ( bi - rads ) category were investigated . mammographic and sonographic findings were available in 21 and 38 pure mc patients , respectively and 5 and 5 mixed type mc , respectively ( table 2 ) . in pure type mc , sensitivity of mammography and sonography was 76.5% and 94.7% , respectively . however , in mixed mc , the sensitivity of mammography and sonography was 100% in both modalities . eighty - five ( 81.7% ) of 104 mc patients had no axillary lymph node involvement and more mc patients had lower tumor stage than idc - nos patients ( p=0.000 and 0.005 , respectively ) . expressions of er and pr were higher in mc than in idc - nos ; 77.3% and 63.2% , respectively , but er only showed a statistical significance ( p=0.008 ) . of the 70 patients whose status of her-2/neu was available , only 10 ( 14.3% ) showed her-2/neu overexpression . tumor size and treatments patterns including operation methods , adjuvant chemotherapy , hormonal therapy , and radiation therapy were not statistically different from idc - nos , but less chemotherapy and more hormone therapy were applied to mc patients due probably to more favorable histologic features associated with higher er expression in mc . clinicopathological characteristics and treatment patterns of pure mc patients are similar to those with the mixed type except tumor size , histologic grade , and radiation therapy ( table 3 ) . more pure mc patients had smaller in size and differentiated histologic grade than mixed type . more radiation therapy was applied to pure mc because more pure mc patients received breast - conserving surgery . the median follow - up duration was 63.5 months in all patients ( range , 0 - 262 months ) . there were 9 disease relapses and 6 deaths during follow - up in mc and 5- and 10-yr disease - free survival ( dfs ) rates were 93.3% and 86.1% , respectively ( fig . five- and 10-yr overall survival ( os ) rates were 93.5% and 86.3% , respectively ( fig . ten - year dfs and os rates of idc - nos were 74.7% and 74.9% , respectively . mc showed better survival outcomes than idc - nos with statistical significance ( fig . 1 , p=0.012 for dfs and 0.005 for os ) . in pure mc , the 10-yr dfs and os rates were 90.2% and 91.3% , respectively and 10-yr dfs and os rates of the mixed type were 68.8% and 100% , respectively . dfs and os rates were not statistically different between pure and mixed types ( fig . 2 , p=0.360 and 0.374 , respectively ) due probably to the small sample size . univariate analysis for dfs and os according to clinicopathological characteristics in mc revealed that lymph node status and tumor stage were statistically significant factors for survival ( table 4 ) . in stage - matched analysis for os this was probably due to the small sample size and short follow - up duration . in age - matched analysis for os , mc showed a better survival rate than idc - nos in the patient group whose age was 50 or younger ( fig . patients whose pathology slide was available for reviewing , survivals of mc according to the subtype were compared with idc - nos ( fig . pure mc showed a better dfs than idc - nos ( p=0.037 ) and there was similar dfs patterns between mixed type mc and idc - nos ( p=0.795 ) . pure mc showed a better os than idc - nos ( p=0.049 ) but differences of os between the mixed type and idc - nos did not reach statistical significance in our study ( p=0.143 ) . it accounted for 16.8% of all female cancers in 2002 and incidence of breast cancer in korean women is anticipated to increase ( 11 , 14 , 15 ) . besides incidence , the percentage of early - stage breast cancer has steadily increased ( 16 ) . screening mammography and use of ultrasonography play an important role in detection of breast cancers in earlier stages ( 17 ) . since 1996 , it was recommended that all korean women over 40 yr old underwent a mammography every 1 or 2 yr ( 18 ) . from 1996 to 2004 , the incidence of stage 0 and i breast cancers increased remarkably by 128.6% and 81.6% , respectively ( 16 ) . however , because of the low incidence rate and small number of studies on specific type of breast cancer including mc , limited information is available regarding epidemiology , clinical , radiological and pathological features , risk factors , and prognosis . it is necessary to investigate incidence rate , clinicopathological characteristics , and prognosis of mc to prepare an adequate treatment guideline . most mc patients complained palpable mass in their breast , and radiologically it frequently mimics a benign lesion ( 19 ) . mc especially appears as a well - defined mass lesion but the mixed type shows an indistinct or microlobulated pattern ( 20 , 21 ) . although image study findings were only available in a small number of patients , 23.5% of pure mc cases had false negative findings in mammography but ultrasonography showed much better sensitivity at 94.7% . among patients available in ultrasonographic findings , these radiologically benign lesion - like characteristics of mc sometimes cause a delay in diagnosis ( 19 ) . physicians must understand the limits of screening mammography because the peak age of incidence in korean breast cancer patients is in the 40s ( 16 ) and the sensitivity of mammography for premenopausal women is quite low ( 22 - 24 ) . middle - aged women presenting breast symptoms should be examined carefully and ultrasonography may be helpful . many western studies reported that mc had more favorable pathological characteristics than idc - nos ( 1 - 4 , 6 , 7 ) . they were smaller in tumor size , less axillary lymph node involvement , more expression rates of er and pr , lower grade , lower proliferation rates and less overexpression of her-2/neu . another characteristic of mc was that it usually occurred in postmenopausal women ( 2 , 4 , 6 ) , and their age at diagnosis ranged from 65 to 71 yr and older than that of idc - nos ranged from 59 to 61 yr ( 3 , 6 ) . the 10-yr os of mc was reported at more than 80% ( 4 , 6 , 7 ) . in our study , the median age of mc patients was younger than idc - nos patients . the median age of our study population was not different from that of korean breast cancer patients and another study reported the mean age of mc and idc - nos at 45.5 and 46.9 yr , respectively , which was similar to our results ( 12 , 25 ) . therefore , the age of onset is quite different from that of western mc cases . the reason for the younger age of onset in korean women is not clear , but it might be partly due to wide use of ultrasonography , genetic or environmental factors , a cohort effect of high incidence in the younger generation or relatively easier accessibility to detect breast cancer among middle - aged women ( 15 ) . however , histological features and survival rates of mc patients were similar to those of western patients . mc of the breast is not a homogeneous entity and was divided into pure and mixed types ( 5 , 10 ) . pure mc was associated with better survival rates than the mixed type , but survival rates of mixed type were not different from those found in idc - nos ( 2 , 26 , 27 ) . among 74 available patients with histologic subtype , there were no differences in dfs and os between pure and mixed mc . this was probably due to the small sample size and short follow - up duration , and larger data samples with longer follow - up would be necessary to confirm these differences . because age distribution was different between mc and idc - nos , we compared survival matched by age . in patients whose age was 50 yr or less , mc showed better survival than idc - nos ( p=0.008 ) . there was a similar trend in patient groups older than 50 yr , although it was not statistically significant ( p=0.349 ) . some western studies reported that age at diagnosis of mc was a significant prognostic factor ( 4 , 6 ) . this may be related to the older onset age in western mc patients . in summary , mucinous carcinoma shows more favorable histologic features and better prognosis than idc - nos . however , korean mc developed at younger ages than idc - nos . since only pure mc showed better prognosis than idc - nos , it is important to differentiate mixed mc from pure mc . patients with mixed mc might be treated as guidelines for idc . in pure mc patients with favorable risk factors , however , adjuvant chemotherapy might be more saved . mc clinically and radiologically mimics a benign lesion and this may lead to a delay in diagnosis . therefore , middle - aged korean women presenting a palpable mass should be examined carefully and the appropriate diagnostic procedures such as ultrasonography are warranted for early detection of malignant tumors .
clinicopathological characteristics and prognostic factors of mucinous carcinoma ( mc ) were compared with invasive ductal carcinoma - not otherwise specified ( idc - nos ) . 
 clinicopathological characteristics and survivals of 104 mc patients were retrospectively reviewed and compared with those of 3,936 idc - nos . 
 the median age at diagnosis was 45 yr in mc and 47 yr in idc - nos , respectively . 
 the sensitivity of mammography and sonography for pure mc were 76.5% and 94.7% , respectively . 
 mc showed favorable characteristics including less involvement of lymph node , lower stage , more expression of estrogen receptors , less her-2 overexpression and differentiated grade , and better 10-yr disease - free survival ( dfs ) and overall survival ( os ) ( 86.1% and 86.3% , respectively ) than idc - nos ( 74.7% and 74.9% , respectively ) . 
 ten - year dfs of pure and mixed type was 90.2% and 68.8% , respectively . 
 nodal status and stage were statistically significant factors for survival . 
 mc in koreans showed similar features to western populations except for a younger age of onset than in idc - nos . 
 since only pure mc showed better prognosis than idc - nos , it is important to differentiate mixed mc from pure mc . 
 middle - aged korean women presenting breast symptoms should be examined carefully and evaluated with an appropriate diagnostic work - up because some patients present radiologically benign - like lesions .