First-line chemotherapy rechallenge after relapse in small cell lung cancer.

Response to second-line therapy in relapsing patients with small cell lung carcinoma (SCLC) is often claimed to be evidence in favour of non-cross resistance. Fifteen patients with SCLC who had relapsed off treatment after responding to initial first-line chemotherapy were retreated with the same regimen at relapse. Ten (67%) achieved a further partial response. Median response duration was only 3 months (range 2-4 months), but similar poor results have been reported for most studies using second-line chemotherapy. Relapse in SCLC does not necessarily imply complete clinical resistance to first-line chemotherapy, and strict clinical criteria are required to demonstrate true non-cross resistance.