Desmoplastic melanoma of the lower lip: A case report in an 82-year-old male

This case report details the diagnosis and management of desmoplastic melanoma (DM) in an 82-year-old male presenting lower lip mass. DM is a rare, aggressive form of melanoma characterized by spindle-shaped cells within a dense fibrous stroma, often making diagnosis challenging due to its amelanotic and indurated nature. The patient presented with a 2cm x 2cm mass. After biopsy, the lesion was confirmed as DM with a Breslow thickness of 5.1mm, indicating advanced disease. The patient underwent wide local excision with reconstructive surgery, partial parotidectomy, and selective neck dissection. Postoperatively, the lesion was re-excised to achieve negative margins. Immunotherapy with Pembrolizumab was initiated due to the stage IIB classification. The patient declined adjuvant radiation therapy but has shown no signs of recurrence on a follow-up PET scan nine months later. This case highlights the diagnostic challenges of DM, especially on the lip, and underscores the importance of early biopsy in atypical lesions. Achieving clear surgical margins is crucial for improving outcomes, as local recurrence is a significant concern. Intraoperatively, frozen sections are not routinely performed on desmoplastic melanoma due to lack of diagnostic value and high rate of false negative. Permanent H&E sections with indicated staining can take 1 to 3 days to obtain results. The multidisciplinary approach, involving surgery, oncology, and radiation therapy, remains essential for optimal patient management. Although the role of adjuvant therapies is still debated, this case contributes to growing evidence suggesting the benefit of adjuvant treatments in reducing local recurrence and improving prognosis. • Desmoplastic melanoma (DM) of the lip is a rare and aggressive subtype, often presenting as a nodular or pigmented lesion, making diagnosis challenging. • Treatment typically involves wide local excision with clear margins due to its tendency to infiltrate deeply, often requiring reconstruction. • Sentinel lymph node biopsy (SLNB) is recommended to assess potential regional metastasis, as DM has a higher risk of nodal spread compared to other melanomas. Early detection and treatment are critical for improving prognosis. • Use of rapid immunohistochemistry (IHC) does not achieve the same sensitivity and specificity as permanent sections utilizing S100 staining. This significantly affects intraoperative planning for the resection of melanoma and may necessitate repeat surgical intervention in the operating room. • Adjuvant radiation therapy can significantly reduce local recurrence rates. • DM treatment with pembrolizumab immunotherapy is found to have a very high response rate making it a promising treatment option for this melanoma subtype.