Concurrent use of multiple low dose chemotherapy agents with differing mechanisms of action as a strategy vs passive resistance: A pilot study.

Resistance may be classified as active (or competitive) (due to excess amount of a factor) vs passive (or non-competitive) (due to a deficiency of a factor). Passive resistance may be important in human solid tumors. In passive resistance, the dose-response curve may be shallow, or may flatten at a relatively low dose. We hypothesized that, if passive resistance were important, it might be advantageous to use low doses of multiple concurrent chemotherapy agents with differing mechanisms of action, rather than using high doses of 2 or 3 drugs. We combined single day cisplatin 60 mg/m2, cyclophosphamide 250 mg/m2, epirubicin 40 mg/m2, paclitaxel 60 mg/m2, and vinblastine 2.5 mg/m2, with 5 days of 5-fluorouracil 200 mg/m2, folinic acid 20 mg/m2 and dexamethasone 4 mg orally q.i.d. every 3 weeks. In later cohorts, doses were escalated, and tamoxifen and verapamil were added. Twenty-three patients were entered. ECOG performance status was 1 in 15 patients and 2 in 8. Number of prior chemotherapy regimens was 0 in 4 patients, 1 in 4, 2 in 8, 3 in 4, 4 in 2, and 7 in 1. Sixteen patients had prior radiotherapy, and 3 had no prior therapy. Myelosuppression and febrile neutropenia were frequent, and 4 heavily pretreated patients died of pneumonia contracted while neutropenic. Diarrhea, nausea and vomiting, and fatigue were also prominent. Among 9 patients with non-small cell lung cancer, one had a partial remission, 4 had stable disease (including 3 with minor objective responses). Two additional non-small cell lung cancer patients also had objective tumor regression, but were coded as failures, since one had tumor progression in <6 weeks and the other died of respiratory failure (thought to be due to severe mucous plugging) one week after his first course of treatment. Among 14 patients with other tumor types, there was one partial response (esophageal carcinoma), 6 patients with stable disease for >6 weeks (including minor responses in one patient each with adenocarcinomas of kidney and breast), and 7 failures (including one patient with adenocarcinoma unknown primary who had minor tumor regression lasting 4 weeks). Despite the unacceptably high toxic death rate, median survival time was 24 weeks (range, 1 week to >104 weeks). This regimen is toxic, but survival duration is longer than would be expected in this heavily pre-treated population. Doses recommended for further study are those used in the first treatment cohort (as described above). Since myelosuppression is the major toxic effect, hemopoietic growth factors might prove helpful with this regimen.