Published online Nov 26, 2025. doi: 10.12998/wjcc.v13.i33.112160
Revised: August 16, 2025
Accepted: October 23, 2025
Published online: November 26, 2025
Processing time: 125 Days and 12.7 Hours
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 lim
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.
This case highlights the potential role of chemoradiotherapy in managing pelvic squamous cell CUP, achieving durable remission in selected patients.
Core Tip: This case report describes an elderly woman with pelvic squamous cell carcinoma of unknown primary (CUP), an entity accounting for less than 1% of CUP cases. A comprehensive diagnostic workup ruled out common primaries, and multidisciplinary evaluation led to chemoradiotherapy with 5-fluorouracil and mitomycin-C plus radiotherapy. The patient achieved complete remission for 12 months with improved functional status. This report emphasizes the value of imaging, pathology, and individualized multidisciplinary management in achieving durable remission in rare pelvic squamous CUP.