Document ID: ./input/supremecourt_opinions/opinions/11pdf/10-1150.pdf
Page Number: 10

6 

MAYO COLLABORATIVE SERVICES v. PROMETHEUS 

LABORATORIES, INC.
 
Opinion of the Court 

increase the amount of said drug subsequently admin­
istered to said subject and
“wherein the level of 6-thioguanine greater than about 
400 pmol per 8x108 red blood cells indicates a need to 
decrease  the  amount  of  said  drug  subsequently  ad­
ministered to said subject.”  ’623 patent, col. 20, ll. 10–
20, 2 App. 16. 

For  present  purposes  we  may  assume  that  the  other 
claims  in  the  patents  do  not  differ  significantly  from
claim 1. 

B 
Respondent,  Prometheus  Laboratories,  Inc.  (Prome­
theus),  is  the  sole  and  exclusive  licensee  of  the  ’623  and 
’302  patents.  It  sells  diagnostic  tests  that  embody  the 
processes the patents describe.  For some time petitioners,
Mayo  Clinic  Rochester  and  Mayo  Collaborative  Services
(collectively  Mayo),  bought  and  used  those  tests.    But  in 
2004 Mayo announced that it intended to begin using and 
selling its own test—a test using somewhat higher metab­
olite  levels  to  determine  toxicity  (450  pmol  per  8x108  for 
6–TG and 5700 pmol per 8x108 for 6–MMP).  Prometheus 
then brought this action claiming patent infringement.

The  District  Court  found  that  Mayo’s  test  infringed 
claim  7  of  the  ’623  patent.    App.  to  Pet.  for  Cert.  110a– 
115a.  In interpreting the claim, the court accepted Prome­
theus’ view that the toxicity-risk level numbers in Mayo’s 
test  and  the  claim  were  too  similar  to  render  the  tests 
significantly different.  The number Mayo used (450) was
too  close  to  the  number  the  claim  used  (400)  to  matter
given appropriate margins of error.  Id., at 98a–107a.  The 
District  Court  also  accepted  Prometheus’  view  that  a 
doctor using Mayo’s test could violate the patent even if he
did not actually alter his treatment decision in the light of 
the test.  In doing so, the court construed the claim’s lan­
guage, “indicates a need to decrease” (or “to increase”), as