Squamous cell carcinoma of unknown primary in the pelvis after complete remission following chemoradiotherapy: A case report.

BACKGROUND

Pelvic squamous cell carcinoma of unknown primary (CUP) is extremely rare, accounting for less than one percent of all CUP cases, and its infrequency has limited the development of standardized diagnostic and treatment guidelines.

CASE SUMMARY: A 77-year-old female with a history of resected lung adenocarcinoma presented with worsening constipation. Imaging revealed a 2.5 cm mass adjacent to the right levator ani muscle. Biopsy confirmed poorly differentiated squamous cell carcinoma, positive for pancytokeratin and p40, and negative for p16, cytokeratin 7, cytokeratin 20, and neuroendocrine markers. No primary lesion was identified despite extensive evaluation. She underwent five cycles of 5-fluorouracil (1000 mg/m2 continuous infusion, days 1-4) and mitomycin-C (10 mg/m2 on day 1) with concurrent pelvic radiotherapy (50.4 Gy in 28 fractions). Follow-up imaging demonstrated complete remission sustained for 12 months. Electrocorticography performance status improved from 2 at diagnosis to 1 during follow-up.

CONCLUSION

This case highlights the potential role of chemoradiotherapy in managing pelvic squamous cell CUP, achieving durable remission in selected patients.