[Immunohistochemical detection of carcinoembryonic antigen and P-glycoprotein in small cell lung cancer at diagnosis and relapse, with special reference to the tissue expression of CEA and response to chemotherapy].

Small cell lung cancer (SCLC) is one of the most sensitive tumors to drug therapy; however, the majority of patients eventually relapse within a few years. Emergence of drug resistance is thought to play a major role in the dismal course of this disease. However, the mechanism of drug resistance in SCLC still remains obscure. Based on the clinical observation that a significant proportion of patients with relapsing tumor show an elevated serum carcinoembryonic antigen (CEA) concentration while serum neuron-specific enolase (NSE) concentration remains normal, we attempted to determine whether the tissue of CEA is indicative of a clonal change in SCLC, in contrast with the tissue expression of NSE and P-glycoprotein (P-gp). We examined 22 SCLC patients with tumor specimens available both at diagnosis and at relapse. Of the 22 patients, two had CEA expression at diagnosis, and a further three patients showed CEA expression at relapse. It is of note that there were two patients whose tumors expressed NSE alone at diagnosis but expressed CEA alone at relapse. Serum CEA concentration was concordant with the tissue expression of CEA; however, serum NSE concentration was not concordant with the tissue expression of NSE. Tumors with CEA expression at relapse were generally resistant to salvage chemotherapy, while there was no close relationship between the tissue expression of P-gp and refractoriness to drugs at relapse. These findings indicate that the tissue expression of CEA in SCLC is a marker of a clonal change during chemotherapy, and such a clonal change would play a role in the emergence of drug resistance in SCLC.