Rare Case of High-Risk Feature Squamous Cell Carcinoma of the Sacrococcygeal Region and its Significant Response to Neoadjuvant Radiotherapy

Summary: Non-HPV squamous cell carcinoma(SCC) of the sacrococcygeal region can be a rare, malignant progression of pilonidal diseases, hidradenitis suppurativa, and other benign conditions. There are case reports that discussed treatment courses that included radiotherapy, surgery, and chemotherapy with varying tumor responses/outcomes. In this case, the patient underwent neo-adjuvant IMRT radiotherapy with nodal boost to high-risk feature SCC refractory to cemiplimab-rwlc treatment with great efficacy in terms of tumor debulking and clinical symptomatology prior to resection. A 54-year-old male presented to his primary care physician for a growing, gluteal mass with ulceration and gluteal cleft extension. He was referred to general surgery for a suspected pilonidal cyst and underwent a Bascom procedure. Pathology demonstrated poorly-differentiated keratinized SCC with necrosis and cystic degeneration with positive, deep margins (P16-,p53+). It also demonstrated pilonidal sinus tract involvement and histologically non-HPV SCC (p16-). He was referred to surgical oncology. Patient underwent PET/CT, demonstrating extensive soft tissue density mass (7.7x6.3x12.9 cm) involving the skin and subcutaneous adipose tissue of the lower posterior pelvis overlying the coccyx. The mass had left medial gluteal musculature involvement, bony coccyx neoplastic infiltrate, and prominent bilateral inguinal nodes. Patient was referred to hematology/oncology for further evaluation. Patient completed a 6-cycle course of neoadjuvant cemiplimab-rwlc therapy. With minimal improvement and interval mass progression, patient was referred to radiation oncology for neoadjuvant radiotherapy prior to resection. After consultation and CT simulation, patient underwent intensity-modulated radiation therapy with bolus. Initially, the patient completed a 5,000 cGy treatment course, 25 fractions over 34 days. After discussions in interdisciplinary tumor-board, patient did not undergo lymph node dissection and completed gluteal/inguinal lymph nodal boost radiotherapy of 2,000cGy, 10 fractions over 10 days. Treatment was successful in tumor debulking and no disease progression, measuring at 1.9x0.8x0.2 cm. Patient underwent radical resection of the SCC and reconstruction with flap. Pathology demonstrated negative margins. Patient has since been followed by consulting services with outpatient follow-ups without complications. Although rare, pilonidal sinus tract, sacrococcygeal SCC should be considered during a complete diagnostic workup of a patient with a sacrococcygeal mass. Despite the lack of tumor response to neo-adjuvant chemotherapy for this patient, there was strong tumor response to the radiotherapy with nodal boost. Multimodal treatment should be considered with pilonidal tract SCC with high-risk features such as bony and muscular local metastasis and invasion. Patients should consider evaluation by radiation and medical oncology concurrently to decrease the time to initiate definitive/neoadjuvant treatment. Lastly, this case demonstrated effective boost treatment in the local region/lymph nodes. Overall, sacrococcygeal SCC arising from the pilonidal sinus tract is a rare disease, and we recommend multidisciplinary oncology involvement to evaluate and treat for optimal tumor response and outcomes. Brian Byun (he/him/his), MD (Presenting Author) - Lakeland Regional Health; Kris Guerrier, MD (Co-Author) - Lakeland Regional Health; Imran Ahmad, MD (Co-Author) - Lakeland Regional Health; Manuel Molina-Vega, MD (Co-Author) - Lakeland Regional Health; Sandra Rodriguez Fernandez, MD (Co-Author) - Lakeland Regional Health