Malignant melanoma of the rectum is an exceedingly rare type of cancer with an aggressive presentation, comprising up to 4% of all anorectal cancers. Presentation of this cancer tends to occur in individuals in their late 80s, with nonspecific symptoms such as anal pain or rectal bleeding. Diagnosing rectal melanoma, especially in early stages, is difficult due to its amelanotic presentation and lack of pigmentation, which results in poor remission rates and prognosis. Furthermore, surgical treatment is difficult as these types of malignant melanomas tend to spread along submucosal planes; thus, complete resections are impractical, especially if caught later. In this case report, we present the radiological and pathological features as seen in a 76-year-old man diagnosed with rectal melanoma. Based on his presentation of a heterogeneous bulky anorectal mass with extensive local invasion, initial impressions were colorectal carcinoma. However, surgical pathology found the mass to be a c-KIT+ melanoma, with positive SOX10, Melan-A, HMB-45, and CD117 biomarkers. While the patient was treated with imatinib, the melanoma was too widespread and aggressive, leading to progression and ultimately death.

中文翻译：

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直肠黑色素瘤：预后严重的罕见癌症。

直肠恶性黑色素瘤是一种极其罕见的癌症，具有侵袭性，占所有肛门直肠癌的 4%。这种癌症往往发生在 80 多岁的人身上，伴有非特异性症状，如肛门疼痛或直肠出血。直肠黑色素瘤的诊断，尤其是早期诊断，由于其无黑色素表现和缺乏色素沉着而很困难，从而导致缓解率和预后较差。此外，手术治疗很困难，因为这些类型的恶性黑色素瘤往往沿着粘膜下层扩散。因此，完全切除是不切实际的，特别是如果后来发现的话。在本病例报告中，我们介绍了一名被诊断患有直肠黑色素瘤的 76 岁男性的放射学和病理学特征。根据他对肛门直肠异质大块肿块的表现，并伴有广泛的局部侵犯，初步印象是结直肠癌。然而，手术病理发现肿块是 c-KIT+ 黑色素瘤，SOX10、Melan-A、HMB-45 和 CD117 生物标志物呈阳性。当患者接受伊马替尼治疗时，黑色素瘤过于广泛且具有侵袭性，导致病情进展并最终死亡。