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

The Risk

 Date of latest revision: 4 Dec 2019

The risk to patients comes in two forms: 1) the chemotherapy agent and 2) the resistance of oncologists to change treatment practices because of the belief that the condition that puts patients at risk is a “rare” genetic condition.


The Chemotherapy Agent: Fluorouracil. The Risk and What Happens When Things Go Wrong


FluoropyrimidineDrugs  (i.e., 5-FU (Fluorouracil™),  oral capecitane-( Xeloda™) have been the primary chemotherapy agent used for many years to effectively treat patients with colon, rectal, and analcancer, and in some cases for patients with breast, and head/neck cancer.  This class of compounds  is used in combinational regimens with other cytotoxics known as: LV-5FU2, FOLFOX4,FOLFOX6, FOLFIRI (digestive cancers),  TPF (Head and Neck Cancers), FEC 100 (Breast Cancers).  Capecitabine can be given either alone or as part of combinational therapy (CAPOX,XELIRI).  Though used for many years, medical journals increasingly point out the risk of its use and are urging care in the administration of fluoropyrimidine drugs (see Research).
Severe toxic reactions affect between 10%-40% of patients and lead to at least 1000 deaths annually in the USA (see Research, Caudle et al., Zhu et al.). Toxic reactions, or adverse events, are graded on a scale of 0, no adverse reaction, to 5, death.  Grade 3 is a severe toxic reaction and a Grade 4 is a life threatening reaction; hospitalization is typical in either Grade 3 or 4 reactions.  Severe side effects may include stomatitis, mucositis, diarrhea, neutropenia, cardiotoxicity and neurotoxicity.  Grade 4 neutropenia with sepsis (whole body inflammation caused by infection) is the most frequent cause of treatment-related deaths with fluoropyrimidine  drugs.
If you or your loved one starts to experience early on the side effects listed above, you MUST report them immediately to your oncologist! Prompt identification and reporting is absolutely essential because the FDA approved antidote used for treating "overdosing" of patients, Vistogard, must be administered within 96 hours of the last dose of the chemotherapy (5-FU). 
Patients with dihydropyrimidine dehydrogenase (DPD) deficiency are at a high risk ofsuffering these severe toxic reactions. In the liver, the DPD enzyme is necessary for the body to metabolize 5-FU into inactive metabolites and keep it from destroying healthy cells.  Normally,more than 90% of the injected dose of 5-FU is rapidly cleared in the liver by DPD, and only a small amount of drug will act as a cytotoxics.  As a consequence, and although variable depending onthe regimens, standard dosing of fluoropyrimidine drugs is normally elevated (e.g., 600 mg/m²/d for 5-FU, and 1250 mg/m²/d for capecitabine) because it takes into account that 90% of the dose isnormally deactivated in the body.   
In most cases, people will not know they suffer this DPD deficiency unless specifically tested, and deficient patients treated with standard dosage may face overexposure to the drug and subsequent severe/lethal toxicities.


Standard Oncological Practice: 5-FU, No Pre-Screening to Detect At Risk Patients


The National Comprehensive Cancer Network (NCCN) provides guidelines widely used for the detection and treatment of cancer (see Help ).  The NCCN holds that "impaired dihydropyrimidine dehydrogenase (DPD) activity is a rare occurrence” (see Petitions).   It, therefore, has not moved to prescribe pre-screening of patients or to reduce the initial dosage of patients. Unfortunately many oncologists hold this same belief and this puts patients at risk.


In addition, genetic tests are generally not part of pre-screening because they cannot reliably predict all the patients at risk.  That is in part because science needs to identify more of the genetic conditions that contribute to DPD deficiency AND because non-genetics factors (e.g. drug to drug interactions and circadian variations) also contribute to compromised DPD activity (see Research, Ciccolini et al./Gamelin et al.).  Screening DPD deficiency on a sole genetic basis is considered as an underpowered strategy today, because the number of patients displaying some known genetic polymorphism is far less than the number of patients displaying severe toxicities upon 5-FU administration, and that epigenetics or non-genetics factors may be unaddressed.


“Functional” tests that detect DPD activity level are used successfully in France to drastically reduce toxicities and fatalities associated with 5-FU or capecitabine  treatments (see Research) but these tests are not yet widely adopted in the USA (see Help).


Reduce Your Risk


Talk with your doctor about the risk of your chemotherapy and how you may reduce it.  Ask your doctor to test your DPD activity level before your first treatment (see Help).  If that type of test is unavailable to your doctor, ask to start with a lower initial dose of 5-FU which the doctor can adjust after monitoring the effects of the drug on you (see Research, Caudle et al. ; Diasio et al., and see Hope). 


Your oncologist may try to dissuade you from pre-screening because it would delay the start of treatment. Stand Firm! Test results can return in a week or two and if you were to start treatment without pre-screening and then suffered a severe toxic reaction, your treatment would be delayed for a longer time or even put off entirely.  The benefit of pre-screening seems pretty clear.


You should also confirm that your oncologist is aware of the antidote, Vistogard, and you should agree upon how you should report symptoms that may present early after treatment and how your doctor will communicate back to you.


Lastly, if you have started treatment and experience signs of toxicity shortly after treatment, report your symptoms immediately because the use of the antidote is only effective within 96 hours of your treatment.


When you have this conversation with your doctor, not only will you be looking out for your health, you will serve to increase awareness of this risk and help shape the future of health care for patients -- pay it forward.