Changing differentiation in small-cell lung cancer after chemotherapy

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