ask about your risk of VERY serious side effects before starting 5-FU Chemotherapy

See Announcements for the great news concerning:

  • A major cancer center's announcement that it will pre-screen patients
  • The FDA's announced drug label change that suggests oncologists consider pre-screening as well as discussing with patients the risk of DPD deficiency and the benefits of testing.


Date of latest revision: 6 Feb 2023




If you have been diagnosed with stage III or IV colon, rectal, or anal cancer, chances are your doctors are discussing with you the need for chemotherapy.  The standard drug for treating these types of cancers is fluorouracil (popularly known as 5-FU); capecitabine (Xeloda) may also be prescribed.


Oncologists have used these drugs for many years in treating gastrointestinal cancers, and in some cases for treating breast, head and neck cancers, and the perception is that they are "fairly well tolerated" by patients.


Wrong!  In fact a significant number of patients  (between 10% -- 40% of treated patients) suffer severe toxic reactions that lead to costly hospital stays and over 1,000 patients will DIE ANNUALLY in the US.


5-FU and capecitabine depend on the patient's body to metabolize the drug quickly to prevent it from damaging healthy cells.  This metabolic process is critically dependent on an enzyme: dihydropyrimidine dehydrogenase (aka DPD).  When a patient's DPD activity is compromised, 5-FU and capecitabine destroy healthy cells and put a person at grave risk.  DPD deficiency presents a single point of failure.  


Most people are unaware of this condition until too late: do not wait until you suffer an adverse reaction. Insist that your oncologist test for the deficiency before starting treatment.


Tests are available to determine if a person has DPD deficiency (see https://test4dpd.org/why-test/) and some cancer centers/clinicians are pre-screening even in the absence of national guidelines (see https://test4dpd.org/leaders-in-the-standard-of-care/#usa).  


You should insist on discussing with your oncologist ways to minimize your risk and to provide you a better outcome before you start chemotherapy.



The goal of this site is to encourage patients suffering colon, rectal, or anal cancer to discuss personalized chemotherapy regimens with their oncologists before starting treatment.   You should not take at face value that the treatment is "fairly well tolerated".


Fluorouracil (also known as 5-FU) and Capecitabine (or Xeloda) have been used for many years as a key chemotherapy agent in the treatment of patients with colon, rectal, anal cancers and is sometimes used to treat head/neck and breast cancer patients.  Oncologists consider this treatment an effective and low risk means of destroying cancerous cells. 


However, medical journals in recent years point to a greater risk of toxic reactions that can lead to hospitalization and, in rare cases, to death.


The intent here is NOT to scare patients, facing cancer is frightening enough, nor to discourage patients from seeking professional medical care.  Instead, the intent is to increase awareness of the risk and to embolden patients and their families to have an educated discussion with their physicians about the risks associated with 5-FU chemotherapy. 


So the following information may prepare you to have a frank discussion with your care provider:


Kathryn received one round of FOLFOX (5-FU, leucovorin, and oxaliplatin) and passed away within 3 weeks (see Personal Stories).  Kathryn inspired many people in our community in many ways and here her inspiration takes form among these pages in the hope that it will achieve one of her last wishes:

"I am optimistic and very grateful to all who have traveled this path before me and contributed to the knowledge and experience of those whose vocation is to heal people like me.  May my experience also contribute to the body of learning."


This site is dedicated to honor her wish and to help others avoid the fate she suffered.

"May my experience contribute to the body of learning."

images: Before and after the treatment that  led to kathryn's death