Clinicopathological and immunohistochemical study of pulmonary neuroendocrine tumors - A single-institute experience

Introduction: Pulmonary neuroendocrine tumors (NETs) comprise a spectrum of tumors ranging from indolent to highly aggressive neoplasm. This study aims to study the clinicopathological and immunohistochemical features of NETs and assess the sensitivity of various IHC markers. Materials and Methods: All consecutive cases of pulmonary NETs diagnosed from January 2016 to June 2019 were analyzed retrospectively. The routine hematoxylin- and eosin-stained sections along with immunohistochemistry (IHC) slides were reviewed. IHC was done using a panel of markers which included synaptophysin, chromogranin, CD56, thyroid transcription factor-1 (TTF-1), p-40, napsin-A, and ki67. Results: Of total number of 53 patients, diagnosis was made on biopsy in 40 patients and resection specimen in 13 patients. Small cell lung carcinoma was the most common (31 cases), followed by 16 cases of typical carcinoid, 5 cases of atypical carcinoid, and 1 case of combined SCLC. Both synaptophysin and chromogranin were positive in all the cases of typical carcinoid. Synaptophysin had better sensitivity than chromogranin in atypical carcinoid and small cell carcinoma. CD56 was positive in 8 out of 9 cases done. TTF-1 was negative in all the cases of typical carcinoid. The sensitivity of TTF-1 in small cell carcinoma was 85.19%. The mean Ki67 labeling index was 1.4%, 6.6%, and 65.6% in typical, atypical carcinoid, and small cell carcinomas, respectively. Conclusion: Synaptophysin was more sensitive than chromogranin, especially in atypical carcinoid and small cell carcinoma. TTF-1 along with high Ki67 differentiates small cell carcinoma from carcinoid.