Histologic transformation from lung squamous cell carcinoma in primary lesion to small cell lung cancer in metastatic lymph node lesion following lobectomy and adjuvant chemotherapy: a case report

Introduction: Lung cancer is the leading cause of cancer death worldwide. Histologic transformation from lung squamous cell carcinoma to small cell lung cancer (SCLC) has become more and more, and its treatment is challenging because of unknown pathogenesis. Presentation of Case: A 62-year-old male patient presented with histologic transformation from primary lesion to metastatic recurrence lesion within 3 years following primary lobectomy and adjuvant chemotherapy. The patient had the symptom of cough at the time of initial illness and recurrence. The primary lesion at the root segment of left superior lobe was diagnosed as lung squamous cell carcinoma without gene mutation (including EGFR, ALK, BRAF V600E, etc.), and recurrence lesion at the swollen lymph nodes in mediastinum (4L group) was diagnosed as SCLC. Up to now, the patient was alive for nearly 4 years after first surgery. Discussion: Surgical resection is the main treatment for lung cancer patient in early stage. Lymph node metastasis is a big threat for the patients in early stage. Recently, the research reports focused on the mechanism and cases of histologic transformation of lung cancer have become more and more. In this case, histologic transformation from squamous cell carcinoma in primary focus to SCLC in metastatic lymph node lesion following lobectomy and adjuvant chemotherapy. However, there was no gene mutation. This is a very unusual report. Conclusion: We analyzed a lung cancer patient with histologic transformation from primary focus to lymphatic metastasis by clinical symptoms, radiologic features, laboratory tests, gene detection, histopathologic characteristics, and immunohistochemical testing. It is helpful to understand the pathogenesis of histologic transformation and metastatic progression for optimizing treatment measures to lung cancer.