The appearance of a second primary lung cancer more than four months after the initial cancer is called a metachronous cancer (as opposed to a synchronous cancer). We provide a case report of an epidermoid carcinoma coming more than three years after the initial diagnosis of an anaplastic small cell cancer of the lung. This second cancer developed in a different territory from the initial lesion. Amongst the hypotheses proposed chemotherapy may through an oncogenic action favour the appearance of a new type of cancer.