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In order to study the mechanisms responsible for resistance to CDDP, 5 human tumor cell lines were made resistant to CDDP by repeated in vitro exposures. After cloning it was found that the cell lines developed were between 3.3-fold and 17-fold more resistant to CDDP than the parental cell lines at the IC90. These lines were also resistant to carboplatin and tetraplatin; however, resistance to tetraplatin was lower than to the other platinum complexes. Sensitivity was also assessed to Adria, MTX, 5-FU, chlorambucil, 4-HC, 4-HIF, BCNU, Thiotepa, HN2, Mito C and L-PAM, and no consistent cross-resistance was observed. As compared with the parental lines, non-protein sulfhydryl content was elevated in 3 resistant lines, and protein sulfhydryl was elevated in all 5 lines, as was glutathione-S-transferase activity. Measurements of platinum in whole cells and nuclei after exposure of the cultures to 25 microM CDDP for either 1 or 6 hr showed that nuclear levels reflected those in whole cells and that, per mg protein, platinum levels were lower in resistant cells at both time points. Formation of DNA cross-links, determined by alkaline elution, was lower in resistant cell lines than in parental cell lines, but did not correlate with the absolute cell kill observed. These results indicate that cellular resistance to CDDP often involves decreases in drug accumulation and increases in protein sulfhydryl content. Possible strategies for overcoming these mechanisms are discussed.

Of 90 patients with intermediate or high-grade sarcoma eligible for a randomized trial of adjuvant doxorubicin (Adriamycin, Adria Laboratories, Columbus, Ohio), 48 were not entered: 24 (27%) by physician's choice and 24 refused randomization. Sixty-five percent of lower stage patients were randomized compared with 37% of those with higher stage (P = .02). Patients with extremity lesions were more frequently offered participation in the study (P = .07). Patients with lower stage lesions accepted randomization more readily than those with higher stage lesions (P = .01). As predicted by the higher stage and percentage of central lesions, the disease-free survival of nonrandomized patients was inferior to that of randomized patients (P = .15). Thus, patients at high risk appeared to avoid randomization and adjuvant doxorubicin in this trial, resulting in an inferior disease-free survival for the nonrandomized control group. Important questions generally require randomized trials that reliably determine relative treatment differences. If, however, the patients in a clinical trial are not representative of the entire patient population because of patient and physician selection biases, the generalizability of the results to the entire patient population may be compromised. For example, the prognosis of the general population cannot necessarily be inferred from the selected group in the study. In this study, the randomized and nonrandomized series yielded differing conclusions regarding treatment efficacy, even when an adjustment was made for known prognostic facts.

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