Saad Shibli Jbour^1,, Malaz Babiker Mustafa², Philipp August Von Breitenbuch³, Omar Bekdache³, Amna Zia Ahmad⁴

Background: Trichoblastic carcinoma is a rare, low-grade malignant tumor arising from hair follicle cells, often presenting in the head and neck region. Diagnosing this tumor can be challenging, especially when it mimics benign lesions such as sebaceous cysts or pilomatricomas. This case report describes an uncommon occurrence of low-grade trichoblastic carcinoma in the lower back, highlighting the diagnostic complexities and management strategies. Case Report: A 51-year-old female with multiple comorbidities, including HIV and HPV 18 and 39 positivity, presented with a chronic lower back swelling and mild pain that had been present for several months. Ultrasound imaging initially suggested a benign lesion such as a sebaceous cyst or pilomatricoma. After excision, histopathological examination revealed a low-grade trichoblastic carcinoma, characterized by basaloid cells, horn cysts, and sebaceous differentiation. The patient underwent a second wide excision due to positive surgical margins, and subsequent pathology confirmed complete tumor removal with no residual malignancy. Discussion: Trichoblastic carcinoma can present as a painless or mildly painful nodule, and its diagnosis is often delayed or misdiagnosed due to its benign clinical appearance. Histopathological analysis remains essential for accurate diagnosis. Although generally low-grade, this carcinoma can show local aggression and recurrence, particularly with positive surgical margins. The role of HPV in the development of skin cancers, especially in immunocompromised individuals, warrants further investigation. Conclusion: Trichoblastic carcinoma should be considered in the differential diagnosis of persistent cutaneous masses, especially those that do not resolve or show growth. Histopathological examination is crucial for diagnosis, and achieving clear surgical margins is essential to prevent recurrence. Regular follow-up is recommended, particularly in patients with HPV positivity.

Trichoblastic carcinoma, Lower back swelling, Malignant tumor, Histopathology, Excision HPV 18 and 39, Diagnosis, Skin cancer, Surgical margins, Immunocompromised patient