Primary Anorectal Amelanotic Melanoma: The First Case Report from Saudi Arabia

Abstract

Anorectal melanomas are exceptionally uncommon and only 30% of anorectal melanomas are amelanotic. We report here a case of an anorectal amelanotic melanoma in a female patient. An 84-year-old patient complained of anal mass for 3 months. On examination, there was a 7.0 cm mass prolapsing through the anus that was pale-pink in color. Abdominal, pelvic, and chest computed tomography (CT) showed rectal wall thickening with an eccentric polypoid soft tissue density mass, and left inguinal and presacral lymph node enlargement along with a small nodule in the lower lobe of the left lung, likely representing metastatic deposit. Microscopic examination revealed a piece of skin with hyperplastic squamous epithelium with surface ulceration. The dermis and underlining tissue were showing infiltration by malignant sheets and nests of ovoid and spindle shape cells with prominent nucleolus and high mitotic s. Immuno-staining for HMB-45, S-100, and Melan-A was positive, and it was negative for P63, CK 5/6, and Pan-CK, thus confirming it as an anorectal amelanotic melanoma, and not an epithelial tumor. This is the first case of an amelanotic anorectal melanoma reported from Saudi Arabia.

A Rare Case of Primary Anorectal Malignant Melanoma

“…Few may have a polyp or hemorrhoid-like presentation. For patients with amelanocytic melanoma, diagnosis is challenging, as these patients are usually initially misdiagnosed as basal cell carcinoma, adenocarcinoma, pyogenic granuloma, or Bowen’s disease [ 6 ]. Our patient had presented with bleeding per rectum and painful defecation.…”

Amelanotic melanoma: A challenging cytological diagnosis- A case series

“…17,18 Patients of amelanotic melanoma have a poor prognosis with 5-year survival rate of less than 20%. 3,19 It is seen that the overall survival rate and progression-free survival rate of patients with pigmented melanoma are higher than in patients with amelanotic melanoma. 20 Cascardi et al have also reported poor prognosis with a 5-years survival rate of 30-35% and a median survival of 36 months.…”

Primary Anorectal Amelanotic Melanoma: Case Report and Review of Literature

“…And upon repeating the immunohistochemistry of anorectal tumor they found positive stains for Melan A, HMB45 and tyrosinase and negative for S100. 5 This highlights the importance of adequate immunohistochemical markers especially if considerable morphologic variability occurs. S100 has high sensitivity (97-100 %) but low specificity (75-85%) whereas HMB45 is highly specific but less sensitive for melanomas.…”

“…3 Therefore, if malignant melanoma is suspected, S100 and both melanoma specific markers HMB45 and Melan A should be done. 5 After the diagnosis of malignant melanoma, it is essential to determine if it is primary or metastatic. The presence of junctional activity beneath squamous epithelium indicates its primary origin like in our case.…”

“…2,3,4 Approximately 30% of anorectal melanomas are amelanotic and hence simulates lymphoma, poorly differentiated carcinoma and GIST on histomorphology. 5,6 Immunohistochemical analysis is often required for the diagnosis of these tumors. 7 Due to rarity of this tumor and sparse data in literature, there is no standardized guidelines for staging and also lacks consensus regarding best therapeutic strategy.…”