Rare small cell lung cancer subtype removed by surgery

What happened, in summary

A man in his 50s with an approximately 40 pack-year smoking history was being treated for high-grade papillary urothelial cancer of the bladder. After transurethral resection and 6 BCG treatments over 3 months, staging CT unexpectedly found a bilobed mass in the right upper lung. Each component measured roughly 3–3.6 cm. PET/CT showed that the mass was metabolically active, but there were no involved lymph nodes or distant metastases. Brain MRI also showed no intracranial spread.

He underwent wedge resection of the lung mass. The tumour’s appearance strongly suggested small cell lung carcinoma, but the pathology was unusual because the cancer cells did not express cytokeratins, markers that are almost always present in this cancer. A broad investigation was needed to exclude lymphoma, melanoma, sarcoma, germ-cell cancer, non-small-cell lung cancer and metastasis from his bladder tumour. The cells showed focal TTF-1 staining and were Napsin A-negative. Molecular tests for EWSR1 and SS18 rearrangements were negative, and electron microscopy demonstrated neurosecretory granules that supported neuroendocrine and small-cell differentiation.

With the diagnosis established as a rare cytokeratin-negative small cell lung carcinoma, he received 4 cycles of adjuvant cisplatin and etoposide after surgery. Follow-up imaging found no residual tumour, recurrence or metastatic disease, and he was doing well.

His case required unusually extensive pathology review because both his prior bladder cancer and the absence of expected cytokeratin staining created realistic alternative diagnoses. The localized presentation also allowed a treatment approach combining surgical resection with adjuvant chemotherapy.