Peripheral neuropathy associated with weekly oral 5-fluorouracil, leucovorin and eniluracil

Dihydromyricetin reverses capecitabine-induced peripheral myelin dysfunction through modulation of oxidative stress

Previous clinical reports have shown that capecitabine, an oral prodrug of 5-fluorouracil (5-Fu), can induce peripheral neuropathy, resulting in numbness, paresthesia and hypoesthesia. However, the mechanism through which capecitabine causes peripheral nerve injury remains unclear. Here, we demonstrate that systemic administration of capecitabine leads to myelin abnormalities in the peripheral nerves of mice, which are possibly attributed to the death of Schwann cells, the myelinating cells in the peripheral nervous system. Furthermore, our results show that 5-Fu induces significant oxidative stress in Schwann cells by inhibiting the expression of the anti-oxidative protein DJ-1, leading to a decrease in Schwann cell markers. We found that the anti-oxidant dihydromyricetin (DMY) reverses 5-Fu-induced Schwann cell death and oxidative stress and alleviates capecitabine-induced myelin abnormalities. Taken together, our data indicate that capecitabine induces peripheral myelin dysfunction by regulating DJ-1-mediated oxidative stress in Schwann cells and reveal DMY as a potential therapeutic strategy for capecitabine-induced peripheral neuropathy.

Focal Neurotoxicity Associated With Topical 5-Fluorouracil

Topical 5-Fluorouracil (5-FU) is an antineoplastic chemotherapy drug used to treat precancerous and cancerous skin growths, such as actinic keratoses (AKs), squamous cell carcinoma in situ, and superficial basal cell carcinoma. The topical agent may rarely cause neurotoxic adverse effects. Multiple cases of systemic 5-FU and capecitabine chemotherapy-induced neuropathies have been reported. However, until now, the topical administration of the drug has not been reported to cause neurotoxicity. We present a case of an 83-year-old male who was prescribed topical 5-FU 5% cream to treat AKs on the left anterior scalp and returned weeks later with the development of focal neurotoxicity in the treatment area. He presented with focal paralysis of the left medial frontalis muscle, with initial loss of sensation followed by intermittent pain and paresthesias, persisting four months after the cessation of therapy. He was referred to a neurologist and received a diagnosis of supraorbital neuralgia. The temporal relationship of symptom onset and the localization of symptoms to the treated area strongly suggests that the medication contributed to the observed neurologic effects. These effects are more likely to be observed in patients with a genetic deficiency of dihydropyrimidine dehydrogenase (DPD), which is responsible for the majority of 5-FU degradation (80%), therefore potentially leading to toxic levels of unmetabolized 5-FU. Providers should be aware of the potentially neurotoxic effects of topical 5-FU in order to properly counsel patients and to consider this as a possible etiology of neurologic deficits in patients using this drug.

ThermoTRP channels in pain sexual dimorphism: new insights for drug intervention

Chronic pain is a major burden for the society and remains more prevalent and severe in females. The presence of chronic pain is linked to persistent alterations in the peripheral and the central nervous system. One of the main types of peripheral pain transducers are the transient receptor potential channels (TRP), also known as thermoTRP channels, which intervene in the perception of hot and cold external stimuli. These channels, and especially TRPV1, TRPA1 and TRPM8, have been subjected to profound investigation because of their role as thermosensors and also because of their implication in acute and chronic pain. Surprisingly, their sensitivity to endogenous signaling has been far less studied. Cumulative evidence suggests that the function of these channels may be differently modulated in males and females, in part through sexual hormones, and this could constitute a significant contributor to the sex differences in chronic pain. Here, we review the exciting advances in thermoTRP pharmacology for males and females in two paradigmatic types of chronic pain with a strong peripheral component: chronic migraine and chemotherapy-induced peripheral neuropathy (CIPN). The possibilities of peripheral druggability offered by these channels and the differential exploitation for men and women represent a development opportunity that will lead to a significant increment of the armamentarium of analgesic medicines for personalized chronic pain treatment.

Nuclear Folate Metabolism

Despite unequivocal evidence that folate deficiency increases risk for human pathologies, and that folic acid intake among women of childbearing age markedly decreases risk for birth defects, definitive evidence for a causal biochemical pathway linking folate to disease and birth defect etiology remains elusive. The de novo and salvage pathways for thymidylate synthesis translocate to the nucleus of mammalian cells during S- and G2/M-phases of the cell cycle and associate with the DNA replication and repair machinery, which limits uracil misincorporation into DNA and genome instability. There is increasing evidence that impairments in nuclear de novo thymidylate synthesis occur in many pathologies resulting from impairments in one-carbon metabolism. Understanding the roles and regulation of nuclear de novo thymidylate synthesis and its relationship to genome stability will increase our understanding of the fundamental mechanisms underlying folate- and vitamin B₁₂-associated pathologies.

First Case of Foot Drop Associated with Capecitabine in a Patient with Thymidylate Synthase Polymorphism

Capecitabine, an oral prodrug of 5-FU, has been approved by the FDA for use in patients with breast and colon cancers. In addition, capecitabine is commonly used in patients with other malignancies such as pancreatic, gastroesophageal, and hepatobiliary tract cancers. Though cerebellar toxicity is a rare but well-known side effect of intravenous 5-FU therapy, peripheral neuropathy with capecitabine has only been described in rare cases. In this case report, we describe a 79-year-old patient with locally advanced adenocarcinoma of the pancreas undergoing chemoradiation therapy with capecitabine who developed peripheral sensorimotor neuropathy. To the best of our knowledge, this is the first patient in the literature who was found to have two mutations (2R) of a 28 base-pair tandem repeat in the 5’ promoter enhancer region (5’-TSER) on both alleles (2R/2R) of thymidylate synthetase (TYMS) gene, possibly responsible for the neurotoxicity.

Prevalence of Oxaliplatin-induced Chronic Neuropathy and Influencing Factors in Patients with Colorectal Cancer in Iran

BACKGROUND

The chemotherapeutic agent oxaliplatin can cause acute and chronic forms of peripheral neuropathy. The aim of this study was to evaluate the incidence of chronic neuropathy and its risk factors in colorectal cancer (CRC) patients treated with FOLFOX or XELOX regimens in the Oncology Ward of Hazrat-e-Rasoul Hospital in Tehran.

MATERIALS AND METHODS

A total of 130 patients with CRC were entered into our study, aged over 18 years, without history of receiving other neurotoxic agents or other predisposing factors such as diabetes or neurologic diseases and kidney and liver dysfunction. For the FOLFOX regimen, patients received oxaliplatin, 85 mg/m2, every 2 weeks for 12 courses and with the XELOX regimen, oxaliplatin was 130 mg/m(2), every 3 weeks for 8 courses. Based on Common Toxicity Criteria (CTC or NCI-CTC v.3), the patients were divided into 5 groups (grades) based on the severity of their symptoms.

RESULTS

Fifty-seven patients (43.8%) were male and 73(56.2%) female. Some 19 patients (14.7%) had BMI<20, 97(74.6%) were between 20-25 and 14 (10.8%) ≥ 25. In 105 patients (80.7%) neuropathy was found. There was significant correlation between BMI, hypomagnesaemia and especially, severity of anemia in patients with neuropathy compared to those without.

CONCLUSIONS

Oxaliplatin regimens can induce chronic neuropathy in CRC patients, with anemia, high BMI and hypomagnesaemia as risk factors that can predispose to this kind of neurotoxicity.

Use of neostigmine in capecitabine-induced paralytic ileus

Paralytic ileus is a recognised side effect of the oral agent capecitabine. We present this report on a patient with metastatic colorectal cancer who was treated with capecitabine and presented with persistent paralytic ileus which did not respond to standard conservative measures. Neostigmine was administered safely, resulting in resolution of the paralytic ileus. This approach merits further investigation.

Peripheral neurotoxicity of oxaliplatin in combination with 5-fluorouracil (FOLFOX) or capecitabine (XELOX): a prospective evaluation of 150 colorectal cancer patients

BACKGROUND

To report our prospective experience on the incidence and pattern of oxaliplatin (OXA)-induced peripheral neuropathy (OXA-IPN) in patients with colorectal cancer (CRC) treated with either FOLFOX-4 or XELoda + OXaliplatin (XELOX).

PATIENTS AND METHODS

One hundred and fifty patients scheduled to be treated with either FOLFOX or XELOX for CRC were prospectively monitored at baseline and followed-up during chemotherapy. The incidence and severity of symptoms secondary to OXA-IPN were recorded using three different types of assessment, i.e. the motor and neurosensory National Cancer Institute common toxicity criteria, version 3.0 (NCI-CTCv3), the clinical version of the total neuropathy score (TNSc) and electrophysiological scores.

RESULTS

Patients treated with either FOLFOX-4 or XELOX manifested similar incidence rates and severities of acute OXA-IPN. However, FOLFOX-4 was associated with increased incidence of chronic neurotoxicity, compared with XELOX-treated patients (n = 64/77 versus 44/73; P = 0.002), at a very similar OXA median cumulative dose during both regimens. Both the NCI-CTCv3 and TNSc demonstrated that the severity of cumulative OXA-IPN in FOLFOX-4-treated patients is higher than in those treated with XELOX.

CONCLUSION

The incidence of acute neurotoxicity during FOLFOX-4 therapy is similar to XELOX. However, it seems that FOLFOX-4 is more neurotoxic than XELOX in terms of cumulative OXA-IPN, despite comparable OXA cumulative dose.

Chemotherapy-induced polyneuropathy. Part I. Pathophysiology

Chemotherapy-induced peripheral neuropathy (CIPN) is a toxic neuropathy, a syndrome consisting of highly distressing symptoms of various degrees of severity. It includes numbness of distal extremities, long-term touch, heat, and cold dysaesthesia and, in more severe cases, motor impairment affecting daily functioning. Each form of the syndrome may be accompanied by symptoms of neuropathic stinging, burning, and tingling pain. In the case of most chemotherapeutic agents, the incidence and severity of CIPN are dependent on the cumulative dose of the drug. The syndrome described is caused by damage to the axons and/or cells of the peripheral nervous system.

Chemotherapeutic agents have distinct mechanisms of action in both neoplastic tissue and the peripheral nervous system; therefore, CIPN should not be regarded as a homogeneous disease entity. The present article is an attempt to systematize the knowledge about the toxic effects of chemotherapy on the peripheral nervous system.

Central and peripheral nervous system toxicity of common chemotherapeutic agents

Central and peripheral nervous system toxicity are frequent complications of most chemotherapy regimens, often leading to reduction of dosages or cessation of the responsible drugs. However, sometimes the afflicted toxicity may not be reversible, especially if it is not recognized early, further compromising the quality of life of the cancer patients. The most common chemotherapeutic agents that might cause CNS toxicity manifested as encephalopathy of various severities include methotrexate, vincristine, ifosfamide, cyclosporine, fludarabine, cytarabine, 5-fluorouracil, cisplatin and the interferons (alpha > beta). Involvement of the peripheral nervous system manifested as distal peripheral neuropathy results after therapy with cisplatin, vincristine, taxanes, suramin and thalidomide. Although several compounds have been proposed as neuroprotective agents, few have been shown to be active against the chemotherapy induced neurotoxicity.

Paralytic Ileus Associated with Capecitabine

Paralytic ileus is a temporary arrest of intestinal peristalsis. We report on two patients with breast cancer who developed paralytic ileus following treatment with capecitabine. The pathophysiology of this disorder and its possible connection to capecitabine are described with the aim of promoting the early recognition of the clinical picture so that unnecessary surgery can be avoided.

Chemotherapy-induced neuropathy

Neurotoxic side effects of cancer therapy are second in frequency to hematological toxicity. Unlike hematological side effects that can be treated with hematopoietic growth factors, neuropathies cannot be treated and protective treatment strategies have not been effective. For the neurologist, the diagnosis of a toxic neuropathy is primarily based on the case history, the clinical and electrophysiological findings, and knowledge of the pattern of neuropathy associated with specific agents. In most cases, toxic neuropathies are length-dependent, sensory, or sensorimotor neuropathies often associated with pain. The platinum compounds are unique in producing a sensory ganglionopathy. Neurotoxicity is usually dependent on cumulative dose. Severity of neuropathy increases with duration of treatment and progression stops once drug treatment is completed. The platinum compounds are an exception where sensory loss may progress for several months after cessation of treatment ("coasting"). As more effective multiple drug combinations are used, patients will be treated with several neurotoxic drugs. Synergistic neurotoxicity has not been extensively investigated. Pre-existent neuropathy may influence the development of a toxic neuropathy. Underlying inherited or inflammatory neuropathies may predispose patients to developing very severe toxic neuropathies. Other factors such as focal radiotherapy or intrathecal administration may enhance neurotoxicity. The neurologist managing the cancer patient who develops neuropathy must answer a series of important questions as follows: (1) Are the symptoms due to peripheral neuropathy? (2) Is the neuropathy due to the underlying disease or the treatment? (3) Should treatment be modified or stopped because of the neuropathy? (4) What is the best supportive care in terms of pain management or physical therapy for each patient? Prevention of toxic neuropathies is most important. In patients with neuropathy, restorative approaches have not been well established. Symptomatic and other management are necessary to maintain and improve quality of life.

Neurotoxicity from oxaliplatin combined with weekly bolus fluorouracil and leucovorin as surgical adjuvant chemotherapy for stage II and III colon cancer: NSABP C-07

PURPOSE

The randomized, multicenter, phase III protocol C-07 compared the efficacy of adjuvant bolus fluorouracil and leucovorin (FULV) versus FULV with oxaliplatin (FLOX) in stage II or III colon cancer. Definitive analysis revealed an increase in 4-year disease-free survival from 67.0% to 73.2% in favor of FLOX. This study compares neurotoxicity between the treatments.

PATIENTS AND METHODS

Neurotoxicity was recorded for all patients using standard adverse event reporting. Patients at select institutions completed a neurotoxicity questionnaire through 18 months of follow-up.

RESULTS

A total of 2,492 patients enrolled onto C-07 and 400 patients enrolled onto the patient-reported substudy. Mean patient-reported neurotoxicity was higher with oxaliplatin throughout the 18 months of study (P < .0001). During therapy, patients receiving oxaliplatin experienced significantly more hand/foot toxicity (eg, "quite a bit" of cold-induced hand/foot pain 26% FLOX v 2.6% FULV) and overall weakness (eg, moderate weakness in 27.4% FLOX v 16.2% FULV). At 18 months, hand neuropathy had diminished, but patients who received oxaliplatin experienced continued foot discomfort (eg, moderate foot numbness and tingling for 22.1% FLOX v 4.6% FULV). Observer-reported neurotoxicity was low grade and primarily neurosensory rather than neuromotor. Sixty-eight percent in the FLOX group v 8% in the FULV group had neurotoxicity at their first on-treatment assessment. Time to resolution was significantly longer for those receiving oxaliplatin, and continued beyond 2 years for more than 10% in the oxaliplatin group.

CONCLUSION

Oxaliplatin causes significant neurotoxicity. It is experienced primarily in the hands during therapy and in the feet during follow-up. In a minority of patients the neurotoxicity is long lasting.

Peripheral neuropathy exacerbation associated with topical 5-fluorouracil

Peripheral neuropathy secondary to 5-flourouracil and capecitabine (Xeloda) has been reported. We report the first case of exacerbation of peripheral neuropathy related to topical 5-flourouracil (Efudex). A 70-year-old Caucasian male with a history of actinic keratosis for 15 years was treated intermittently with topical application of 5-flourouracil. He also developed sensory peripheral neuropathy around the same time, but extensive work-up disclosed no clear etiology. In early 2005, he developed an exacerbation of his peripheral neuropathy following a 21-day course of topical 5-flourouracil for actinic keratosis, especially pain and parasthesias. Dihydropyrimidine dehydrogenase activity was evaluated in the peripheral mononuclear cells both by radioassay and by [2-C] uracil breath test. Dihydropyrimidine dehydrogenase activity was within the normal range by both methods. Stopping topical 5-flourouracil resolved the symptoms to baseline. Instead of topical 5-flourouracil, topical imiquimod was used which did not exacerbate his neuropathy. He was not re-challenged with topical 5-flourouracil. Topical 5-flourouracil has been known to cause mainly dermatological adverse effects, but systemic effects because of absorption are possible, especially in dihydropyrimidine dehydrogenase-deficient patients. As our patient had no other cause responsible for his neuropathy, the onset of symptoms coincided historically with topical application of 5-flourouracil and the 5-flourouracil usage preceded an exacerbation of sensory symptoms, we conclude that this drug was responsible for his polyneuropathy.

Survey of oxaliplatin-associated neurotoxicity using an interview-based questionnaire in patients with metastatic colorectal cancer

Background

New chemotherapy regimens for patients with colorectal cancer have improved survival, but at the cost of clinical toxicity. Oxaliplatin, an agent used in first-line therapy for metastatic colorectal cancer, causes acute and chronic neurotoxicity. This study was performed to carefully assess the incidence, type and duration of oxaliplatin neurotoxicity.

Methods

A detailed questionnaire was completed after each chemotherapy cycle for patients with metastatic colorectal cancer enrolled in a phase I trial of oxaliplatin and capecitabine. An oxaliplatin specific neurotoxicity scale was used to grade toxicity.

Results

Eighty-six adult patients with colorectal cancer were evaluated. Acute neuropathy symptoms included voice changes, visual alterations, pharyngo-laryngeal dysesthesia (lack of awareness of breathing); peri-oral or oral numbness, pain and symptoms due to muscle contraction (spasm, cramps, tremors). When the worst neurotoxicity per patient was considered, grade 1/2/3/4 dysesthesias and paresthesias were seen in 71/12/5/0 and 66/20/7/1 percent of patients. By cycles 3, 6, 9, and 12, oxaliplatin dose reduction or discontinuation was needed in 2.7%, 20%, 37.5% and 62.5% of patients.

Conclusion

Oxaliplatin-associated acute neuropathy causes a variety of distressing, but transient, symptoms due to peripheral sensory and motor nerve hyperexcitability. Chronic neuropathy may be debilitating and often necessitates dose reductions or discontinuation of oxaliplatin. Patients should be warned of the possible spectrum of symptoms and re-assured about the transient nature of acute neurotoxicity. Ongoing studies are addressing the treatment and prophylaxis of oxaliplatin neurotoxicity.

Monitoring fluoropyrimidine metabolism in solid tumors with in vivo (19)F magnetic resonance spectroscopy

(19)Fluorine magnetic resonance spectroscopy ((19)F MRS) offers unique possibilities for monitoring the pharmacokinetics of fluoropyrimidines in vivo in tumors and normal tissue in a non-invasive way, both in animals and in patients. This method may therefore be useful for predicting response to fluoropyrimidine-based therapy with or without the effects of modulating agents, and this may be of value for the individualization of anticancer therapy and the strategic development of new anticancer drugs. (19)F MRS has been very valuable in elucidating the basic aspects of fluoropyrimidine metabolism, especially in animal studies. Studies in humans have indicated its clinical potential, but widespread application has been hampered by the relatively low detection sensitivity of the method. The recent introduction of clinical MR scanners with magnetic fields above 1.5 T may stimulate increased clinical use of (19)F MRS.

Peripheral neuropathy associated with capecitabine

5-fluorouracil (5-FU)-associated peripheral neuropathy is an uncommon event. Capecitabine (CAP) is a pro-drug of 5-FU and peripheral neuropathy associated with CAP has not been reported. During analysis of 28 patients receiving CAP with concomitant radiation (XRT) for pancreatic cancer (resected or locally advanced), two patients developed signs and symptoms consistent with peripheral neuropathy. Patients received CAP 1200-1600 mg/m2 in two divided doses with XRT (total 5040-5400 Gy) x 6 weeks, followed by 4 weeks rest, then 6 cycles of CAP 2000-2500 mg/m2 in two divided doses x 14 days every (q) 3 weeks. Patients were assessed weekly during CAP-XRT and q 3 weeks during CAP alone. Patient A reported right leg weakness (foot drop) during week 4 of CAP-XRT (1600 mg/m2). Patient B developed perioral and upper extremity paresthesias during the fourth cycle of CAP alone (2500 mg/m2). Dihydropyrimidine dehydrogenase (DPD) activity was measured by radioisotopic assay using lysates of peripheral blood mononuclear cells. Neurologic examination revealed right foot drop in Patient A and was unremarkable in Patient B. Central nervous system imaging was negative. Electromyogram and nerve conduction studies showed sensorimotor peripheral neuropathy in both patients. DPD activity was normal in both patients. There was no evidence of disease progression. Neurologic symptoms resolved after stopping CAP for 4 weeks in Patient A, with no recurrence after reinitiating CAP alone at 2000 mg/m2. Patient B continued at 80% of standard dose (2000 mg/m2) and symptoms resolved without further intervention. We conclude peripheral neuropathy with 5-FU is rare. Neurotoxicity occurs most often with intermittent high dose 5-FU as bolus injection or 24- to 48-h infusions. The etiology of neurotoxicity in our two patients remains unclear; however, as CAP is rapidly metabolized to 5-FU in patients with normal liver function, it is likely that 5-FU or its active metabolites (fluoro-beta-alanine) were contributing factors. Knowledge regarding potential adverse effects of CAP is paramount and dose modification is indicated with development of neurotoxicity.

Neurotoxic complications of chemotherapy in patients with cancer: clinical signs and optimal management

Neurotoxic side effects of chemotherapy occur frequently and are often a reason to limit the dose of chemotherapy. Since bone marrow toxicity, as the major limiting factor in most chemotherapeutic regimens, can be overcome with growth factors or bone marrow transplantation, the use of higher doses of chemotherapy is possible, which increases the risk of neurotoxicity. Chemotherapy may cause both peripheral neurotoxicity, consisting mainly of a peripheral neuropathy, and central neurotoxicity, ranging from minor cognitive deficits to encephalopathy with dementia or even coma. In this article we describe the neurological adverse effects of the most commonly used chemotherapeutic agents. The vinca-alkaloids, cisplatin and the taxanes are amongst the most important drugs inducing peripheral neurotoxicity. These drugs are widely used for various malignancies such as ovarian and breast cancer, and haematological cancers. Chemotherapy-induced neuropathy is clearly related to cumulative dose or dose-intensities. Patients who already have neuropathic symptoms due to diabetes mellitus, hereditary neuropathies or earlier treatment with neurotoxic chemotherapy are thought to be more vulnerable for the development of chemotherapy-induced peripheral neuropathy. Methotrexate, cytarabine (cytosine arabinoside) and ifosfamide are primarily known for their central neurotoxic side effects. Central neurotoxicity ranges from acute toxicity such as aseptic meningitis, to delayed toxicities comprising cognitive deficits, hemiparesis, aphasia and progressive dementia. Risk factors are high doses, frequent administration and radiotherapy preceding methotrexate chemotherapy, which appears to be more neurotoxic than methotrexate as single modality. Data on management and neuroprotective agents are discussed. Management mainly consists of cumulative dose-reduction or lower dose-intensities, especially in patients who are at higher risk to develop neurotoxic side effects. None of the neuroprotective agents described in this article can be recommended for standard use in daily practise at this moment, and further studies are needed to confirm some of the beneficial effects described.

The effect of dihydropyrimidine dehydrogenase deficiency on outcomes with fluorouracil

The use of fluorouracil has been complicated by unpredictable pharmacokinetics, low response rates and seemingly random toxicity. The variable pharmacology is largely due to inherited differences in expression of the metabolising enzyme dihydropyrimidine dehydrogenase (DPD). This converts fluorouracil to inactive metabolites (catabolic pathway) and ultimately dictates the amount of fluorouracil that is available to be metabolised to cytotoxic nucleotides (anabolic pathway). Absolute and partial DPD deficiency affect around 0.1 and 3% of the Caucasian population, respectively. Administration of conventional doses of fluorouracil to these individuals has resulted in profound bone marrow and gastrointestinal toxicity, especially in those with absolute DPD deficiency. Other forms of toxicity such as myocardial ischaemia have been difficult to attribute directly to DPD deficiency. Efforts to improve outcomes with fluorouracil have included monitoring of fluorouracil concentrations and modifying fluorouracil administration techniques (e.g. from bolus injections to protracted intravenous infusions). In general, these moves have met with limited therapeutic advancement. The recognition that DPD deficiency increases toxicity has lead to the suggestion that genotypic or phenotypic assessment of DPD status prior to initiating fluorouracil may help predict outcomes. The gene that encodes for DPD expression is called DPYD. Approximately 1% of Caucasians are heterozygotes for the DPYD*2A mutation which is the variant allele that is most frequently implicated in DPD deficiency. Screening for this mutation may identify around 60% of individuals with absolute DPD deficiency who are at the greatest risk of toxicity. Another approach is to determine DPD activity in peripheral blood mononuclear cells, with low activity suggesting an increased risk of toxicity. Intratumoral DPD activity may also be assessed with high activity suggesting a poorer response to fluorouracil. Recently, drugs that inhibit DPD (e.g. eniluracil) have become available. These remove much of the variability in fluorouracil pharmacokinetics and may make assessment of DPD activity redundant. Despite the considerable inroads that have been made, further study is needed before the best means of optimising fluorouracil treatment is determined.