First case report of immune checkpoint inhibitor therapy to treat secretory carcinoma.

Secretory carcinoma (SC) is a newly defined and exceedingly rare pathologic subtype of lung cancer. We present a case of SC that was initially misdiagnosed as stage IIIB (cT2aN3M0) invasive mucinous adenocarcinoma harboring a programmed cell death ligand 1 tumor proportion score of 10% and an ETV6-MET fusion gene. The patient received five cycles of toripalimab and pemetrexed plus carboplatin at a local hospital without treatment-related adverse events. Radiologic evaluations prior to third- and fifth-cycle immunochemotherapy indicated that the best response was stable disease. The patient was subsequently reclassified as having stage IB (cT2aN0M0) primary pulmonary malignancy after invasive N staging at our institution, and the primary tumor and mediastinal lymph nodes were removed via a thoracoscope. The tumor exhibited typical morphologic features of SC with immunohistochemical positivity for Mammaglobin and S100 but not for NapsinA or TTF1. Tumor regression was scarcely observed in the surgically resected specimens. This patient was the fifth reported case of primary SC of the lung and the first case of SC treated with immune checkpoint inhibitor therapy that was evaluated in terms of comprehensive safety and efficacy.