[Squamous cell carcinoma of the lung in a patient treated for small cell carcinoma. Does chemotherapy encourage the development of histologically different tumour? (author's transl)].

A 60-year-old male patient with small carcinoma of the lung was treated with chemotherapy and radiotherapy. The tumour regressed, but two squamous cell carcinomas appeared in the contralateral lung. The first one was discovered after 3 months' treatment and developed slowly; the second one, diagnosed after 9 months' treatment, was rapidly progressive. The patient died 13 months after the beginning of treatment, and only the squamous cell carcinomas could be confirmed on autopsy. Such cases may reflect either selection of tumours that were present from the beginning of treatment, or development of other malignancies, or treatment-induced histological changes in the original tumour.