Synchronous multiple lung cancers with hilar lymph node metastasis of small cell carcinoma: A case report

BACKGROUND: Synchronous multiple lung cancers are rare and refer to the simultaneous presence of two or more primary lung tumors, which present significant challenges in terms of diagnosis and treatment. CASE SUMMARY: We report a case of multiple synchronous lung cancers with hilar lymph node metastasis of small cell carcinoma of unknown origin in a 73-year-old man. Transbronchial lung biopsy revealed squamous cell carcinoma. Although enlargement of lymph node 12u was detected, no distant metastases were observed. The patient was preoperatively diagnosed with T1cN0M0 and underwent thoracoscopic right upper lobectomy with nodal dissection (ND2a). Based on histopathological findings, the primary lesion was squamous cell carcinoma. A microinvasive adenocarcinoma was also observed on the cranial side of the primary lesion. Tumors were detected in two resected lymph nodes (#12u and #11s). Both tumors were pathologically diagnosed as small cell carcinomas. The primary lesion of the small cell carcinoma could not be identified even by whole-body imaging; however, chemotherapy was initiated for hilar lymph node metastasis of the small cell carcinoma of unknown origin. CONCLUSION: Multiple synchronous lung cancers can be accompanied by hilar lymph node metastasis of small cell carcinomas of unknown origin.