[Changes in differentiation of small cell lung cancer after chemotherapy]

We reexamined biopsy and resection specimens from seven patients with histologically established primary diagnosis of small-cell lung cancer (SCLC) which showed previously undetected adenocarcinomatous differentiation after chemotherapy. Adenocarcinoma was diagnosed in the same part of the lung as was SCLC before treatment in five cases and in contralateral location in two. Two tumors showed heterogeneous differentiation with small-cell and adenocarcinomatous components, and five had only adenocarcinoma. The interval between histological evidence of SCLC and adenocarcinoma was 3 months-5 years. From the specific findings in the respective patients we can offer two possible explanations for changing differentiation in SCLC after chemotherapy: (a) a primarily heterogeneously differentiated tumor with selection of adenocarcinomatous component under chemotherapy, and (b) an independently developed adenocarcinoma after successful chemotherapy of SCLC, as patients with treated SCLC are known to have an increased risk of non-SCLC. However, therapy-induced alteration of differentiation seems much more unlikely. These findings should be considered in diagnosis and therapy of SCLC to allow early and appropriate reaction to non-SCLC components.