Population study of dihydropyrimidine dehydrogenase in cancer patients

We conducted a prospective study on a large set of cancer patients in an attempt to evaluate the incidence of complete or partial dihydropyrimidine dehydrogenase (DPD) deficiency as found in peripheral mononuclear cells (PMNC).

One hundred eighty-five unselected consecutive cancer patients were included. The population consisted of 152 men (mean age, 62.1 years; range, 35 to 90) and 33 women (mean age, 59.2 years; range, 36 to 77). Sixty-eight were head and neck patients treated by a 5-day continuous infusion of fluorouracil (FU; starting dose, 1 g/m2/d, with dose adaptation based on pharmacokinetics) for which DPD activity was measured 2 to 3 days before FU administration (94 cycles analyzed). PMNC-DPD activity was measured by a radio-enzymatic assay using carbon-14-FU.

DPD activity in the entire population showed a unimodal distribution, which globally fits a gaussian distribution. Mean and median DPD activity values were 0.222 and 0.211 nmol/min/mg protein, respectively (range, 0.065 to 0.559). No total DPD deficiency was found. Multifactor analysis of variance showed that liver function (biologic evaluation) and age did not influence DPD activity, but that DPD activity was, on average, 15% lower in women (0.194 nmol/min/mg protein) than in men (0.228 nmol/min/mg protein) (P = .03). No difference was demonstrated between premenopausal and postmenopausal women. In patients treated with FU, the risk of developing side effects was not linked to pretreatment DPD activity. FU-related toxicity was linked to FU systemic exposure. The correlation between pretreatment DPD activity and FU systemic clearance (CI) was weak (n = 90, linear regression r = .31, P = .002). Pretreatment DPD activity in patients who required a dose reduction was not significantly different from DPD activity in patients who did not require dose modification.

From the present study, it appears that total DPD deficiency is a rare event. Although pretreatment DPD activity cannot be a useful indicator for improving FU dose adaptation strategy, the identification of severe DPD deficiency (< 0.100 nmol/min/mg protein) could lead to starting the treatment with a markedly reduced FU dose or even to using an alternative chemotherapy regimen.