Activity of sequential low-dose methotrexate and fluorouracil in advanced colorectal carcinoma: attempt at correlation with tissue and blood levels of phosphoribosylpyrophosphate.

Forty-five patients with metastatic colorectal carcinoma were treated with low-dose methotrexate (MTX) and 5-fluorouracil (5-FU) given sequentially. The dose of MTX was 40 mg/m2 intravenously (IV) on days 1 and 8 followed 24 hours later by 5-FU at 600 mg/m2 IV on days 2 and 9; the drugs were recycled every 28 days. Fourteen (32%) of 43 adequately treated patients had a complete or partial response lasting a median of nine months (range, 6-15 + months). Four patients had a minor response and seven patients had stable disease for a median of nine and 10 months, respectively. Toxicity included mucositis in 28 (65%) patients, diarrhea in 18 (40%), nausea in 11 (24%), and vomiting in seven (16%). Hematologic toxicity was mild: six patients had nadir white blood cell counts less than 3.5 X 10(3) cells/microL, and seven patients had a nadir platelet count less than 100 X 10(3) cells/microL. Serial biopsies and blood samples were obtained in selected patients to evaluate the effect of MTX on tissue and lymphocyte phosphoribosylpyrophosphate (PRPP) and PRPP synthetase levels.