We report two cases of rectal malignant melanomas. The patients were an 84-year-old male and a 66-year-old female who had blood in their stools. They were preoperatively diagnosed with poorly differentiated adenocarcinoma of the rectum. The clinical diagnosis for each was rectal carcinoma at stage IIIc according to the tumor-node-metastasis classification (6th edition), and the patients underwent abdominoperineal resection with dissection of lymph nodes. Pathological examination of the resected specimens revealed a malignant melanoma. Immunohistochemical analysis results were positive for HMB-45 and negative for cytokeratin AE1/AE3, CD45, and synaptophysin. Primary anorectal melanoma is an uncommon and aggressive disease that carries a poor prognosis. Therefore, it is necessary to provide systemic treatment. To improve prognosis, it is important to detect anorectal melanoma at an early stage.
Anorectal melanoma is an uncommon and aggressive disease. The anorectum is the third most common location of malignant melanoma after the skin and retina. The most common symptom is rectal bleeding, which is often mistaken for bleeding associated with hemorrhoids. Diagnosis is very difficult, and initial diagnosis may be incorrect in 80% of all cases [
An 84-year-old male was referred to our hospital with the chief complaint of bloody stool. Digital examination of the rectum revealed a hard mass at the 9 o’clock position. Colonoscopy revealed an irregular surface mass with a diameter of approximately 60 mm, located on the right wall of the lower rectum, 30 mm from the anal verge. Biopsy of the rectal mass was performed, and histopathological examination showed poorly differentiated adenocarcinoma. Computed tomography (CT) showed a thickening of the rectal wall and lymph node swelling of the circumference of an internal iliac artery; however, there was no evidence of distant metastasis (Figure
Case 1 CT, FDG-PET, MRI, and pathological imaging. (a) CT shows that the tumor into the lumen. (b) FDG-PET shows that increased accumulation of FDG. (c) Macroscopic image of the rectal tumor showing pigmented lesions. (d) Histopathological examination of the rectal specimen showed the nest of melanocytic cells (e.g., HE stain, ×40). (e) Rectal specimen is positive for the expression of HMB-45 (×20). (f) CT shows multiple liver metastases.
The clinical diagnosis was rectal carcinoma at stage IIIc according to the tumor-node-metastasis (TNM) classification (6th edition). The patient was treated by abdominoperineal resection (APR) with dissection of lymph nodes. The resected specimen showed some pigmented lesions within the tumor and around the anal verge (Figure
Three months after the resection, the patient was rehospitalized with a chief complaint of right leg edema and dyspnea. Laboratory data showed liver and renal dysfunction. CT showed multiple liver and right inguinal lymph node metastases (Figure
A 66-year-old female was referred to our hospital with the chief complaint of blood in the stool. Digital examination revealed a hard mass located all around the wall, 1.0 cm from the anal verge. Colonoscopy revealed an irregular surface large mass of approximately 80 mm in diameter located all around the wall of the lower rectum, 10 mm from the anal verge. Histopathological examination showed features of poorly differentiated adenocarcinoma. CT and MRI revealed an increased density in the perirectal area, rectal wall thickening all-around, and regional lymph node metastases. DWI produced a high signal in the previously described area. Laboratory data as well as CEA and CA19-9 levels were almost normal. The boundary with the vaginal wall was unclear. Under the diagnosis of stage IIIc rectal carcinoma according to the TNM classification (6th edition), we performed an APR with dissection of lymph nodes. Because there was invasion of the vagina, a part of the vagina was also resected at the same time. The resected specimen revealed some pigmented lesions within the tumor and around the anal verge (Figure
Case 2 pathological imaging. (a) Macroscopic image of the rectal tumor showing some pigmented lesions. (b) Rectal specimen is positive for the expression of HMB-45 (×20).
Histopathological examination showed the characteristics of malignant melanoma. Immunohistologically, the results showed positive expression of HMB-45 (Figure
Malignant melanoma of the rectum is rare and has very poor prognosis. The incidence has been reported to be 0.4%–3.0% of all malignant melanoma and 0.1%–4.6% of all anorectal malignant tumors [
For anorectal malignant melanoma, multimodality treatments including surgery, chemotherapy, and radiotherapy have been used. Surgery is the main treatment. The surgical procedure varies from WLE to APR. However, the relative benefit of these individual procedures is unclear [
The tumor tends to be quite radiotherapy resistant and shows a poor response to chemotherapy [
In conclusion, anorectal melanoma is a rare and aggressive disease. Because of nonspecific symptoms, it is easily mistaken for hemorrhoids. Because malignant melanoma occurs frequently in the anorectum, clinicians should suspect anorectal melanoma in cases presenting with blood in the stool. Furthermore, the prognosis depends on the staging, and it is important to detect anorectal melanoma at an early stage. Ultimately, the development of further effective adjuvant therapy may improve the survival rate.
The authors thank the patients and this paper has not been published previously.