Anorectal melanoma: report of three cases with extended follow-up.

Abstract: Primary anorectal melanoma is rare. There is controversy regarding the best surgical treatment because of its poor prognosis. Three cases with extended follow-up are reported in this article. A 53-year-old woman with rectal bleeding was diagnosed with a melanoma of the rectum and underwent an abdominoperineal resection. The patient died with distant metastases 8 months later. An 80-year-old woman with rectal bleeding was diagnosed with a melanoma of the rectum and underwent a transanal local excision. She remains alive 4 years later but with locally recurrent disease. A 78-year-old man with rectal bleeding was diagnosed with a melanoma of the rectum and underwent an abdominoperineal resection. He died with local and metastatic disease 25 months later. Recent trends favor local excision when technically feasible, although some patients may require an abdominoperineal resection of the rectum, especially for larger tumors.

Key Words: anus, melanoma, rectum, surgical treatment, tumors

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Primary anorectal melanoma (ARM) is a rare disorder. It constitutes less than 1% of all melanomas and 4% of all anorectal tumors other than adenocarcinoma. (1) The absence of early clinical manifestations and the lack of clinical suspicion due to its infrequency contribute to delayed diagnosis. (2,3) Up to 60% of patients have been found to have metastatic disease at the time of diagnosis. (4) The optimal surgical treatment for ARM is controversial and difficult to demonstrate, partly because there are few series, usually with a small number of patients, and most information comes from case reports without complete follow-up. Abdominoperineal resection (APR) of the rectum results in a lower local recurrence rate than local excision. (1,5) However, the incidence of subsequent distant metastases is similar, and the survival rate remains poor. (1-9) In the present article, three patients with ARM who underwent surgical treatment and who have extended follow-up are reported with the objective of analyzing the clinical presentation, histopathologic features, treatment, and long-term outcome.

Case Reports

Patient 1

A 53-year-old woman presented with a 2-month history of diarrhea, rectal bleeding, and transanal mucous discharge. At physical exploration, a mass in the lower rectum was palpated. There was no clinical involvement on the inguinal nodes. At rectosigmoidoscopy, a 6-cm, polypoid, ulcerated, pigmented tumor of the lower third of the rectum was found that on biopsy was proved to be melanoma. There was no evidence of metastatic disease. The patient underwent an APR. The histopathologic study showed a melanoma with invasion through the muscularis propria (Fig. 1), colonic glands were observed between the tumor and the stratified epithelium of the anus (Fig. 2), and 1 of 22 pericolic lymph node was positive. Staining for S-100 and HMB45 was positive. Six months after the operation, liver and lung metastases and pelvic recurrence of disease were documented, and the patient died 2 months afterward.

Patient 2

An 80-year-old woman presented with a 1-month history of rectal bleeding, malaise, and weight loss. A colonoscopy demonstrated a pigmented 3-cm tumor in the lower rectum. The biopsy demonstrated ARM. There was no clinical inguinal involvement. Metastatic disease was ruled out. The patient underwent a wide transanal full-thickness local excision. The histopathologic findings showed neoplastic cells with melanin in the cytoplasm and dysplastic nucleus in the lamina propria invading into the submucosa. Staining for S-100 and HMB45 was positive. Recurrent disease localized to the lower rectal and perirectal area was demonstrated 2 years later, without clinical inguinal involvement. The patient refused an APR and/or any alternative of adjuvant treatment, and underwent an incomplete transanal local excision. Two years afterward, the patient remains alive, with minimal anal bleeding and pain due to local recurrent disease localized in the anorectal area, and without distant metastases.

Patient 3

A 78-year-old man presented with a 4-month history of diarrhea, rectal bleeding, diffuse abdominal pain, and weight loss. At physical exploration, a nodular mass 4 cm from the anal verge was palpated. There was no clinical involvement of inguinal nodes. A colonoscopy showed a 5 X 5-cm ulcerated exophytic mass. Biopsy specimens proved to be melanoma. There was no evidence of metastatic disease. The patient underwent an APR. On histopathology, large neoplastic cells with melanin in the cytoplasm invading into the muscular layer and one positive lymph node were found. Staining for S-100 and HMB45 was positive. The patient underwent adjuvant treatment with interferon alfa-2b (20 million IU/[m.sup.2] administered IV 5 d/wk for 4 weeks; and 10 million IU/[m.sup.2] administered SC three times per week for 48 weeks). Metastatic disease to the liver and inguinal nodes was demonstrated 19 months later, and the patient died 6 months afterward.

Discussion

The existence of primary rectal melanomas has been controversial, but possibly has been clarified with the demonstration of normal melanocytes proximal to the dentate line, even in the rectal mucosa. (10-12) Accordingly, Figure 1 shows the pigmented tumor originating in the rectum and sparing the mucosa of the anal canal. Similar to the present cases, ARM is usually diagnosed in advanced decades of life, with a slightly higher preponderance in women, and with rectal bleeding as the main symptom. (1-9) Once a rectal or anal mass is documented, pigmentation may be one of the clues for the identification of ARM (Fig. 1); (13) however, macroscopic pigmentation may not always be present. (4,14) After diagnosing ARM, the workup should be guided by clinical symptoms that could suggest metastases and should include computed tomographic scan of the abdomen and pelvis, and thorax films.

[FIGURE 1 OMITTED]

There is controversy regarding the best surgical treatment. Unfortunately, survival seems to depend on staging and does not seem to be modified by surgical radicality, (5,15-17) because most patients develop metastatic disease and die after relatively short intervals. (1,5,6) Aggressive surgical management has included APR and/or posterior pelvic exenteration, (14-18) and has been recommended by some authors stating that this may be the only means of obtaining long-term survival. However, long survivals have also been found after transanal local excision, and no difference in survival has been demonstrated after APR or local excision when patients are compared by similar stages. (1-4,6-8,15,19-21) Because transanal local excision has less morbidity than APR and avoids the necessity of a colostomy, most authors consider it as the first choice of treatment for ARM when it is technically feasible. (2-4,6-8,15,19-22) Recently, Ballo et al (23) demonstrated that adjuvant radiation can help to control locoregional disease in patients with local excisions for ARM. Although the patients of our report were operated on before this report, these data justify adjuvant treatment with radiation in patients with ARM submitted to local excision.

[FIGURE 2 OMITTED]

The results of our cases reflect the data previously commented on. Patient 1 underwent an APR with curative intent, but died with metastatic disease after a short period. Patient 2 was an elderly patient who underwent a transanal local excision with a short hospitalization period and without morbidity; there was recurrent disease 2 years later, but although the patient refused further surgical or adjuvant treatment, she continues alive 2 years after recurrent disease was evident. Patient 3 was also an elderly patient who underwent an APR for a large tumor, underwent adjuvant treatment with interferon alfa-2b, but also developed recurrent disease and died approximately 2 years later. These cases reflect well how the prognosis seems most dependent on the biologic behavior of the tumor and/or stage rather than on the surgical operation or adjuvant treatment.

Conclusion

ARM is a rare disorder. The prognosis is poor and surgical management should be the least morbid: a wide local excision when technically feasible, and a combined APR for large or obstructing tumors.

Accepted July 24, 2003.

Copyright [c] 2004 by The Southern Medical Association

0038-4348/04/9703-0311

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RELATED ARTICLE: Key Points

* Primary anorectal melanoma is a rare disorder.

* The optimal surgical treatment is controversial because the prognosis is poor.

* Local excision is the preferred treatment over abdominoperineal resection of the rectum.

Takeshi Takahashi, MD, FACS, Liliana Velasco, MD, Xeily Zarate, MD, Heriberto Medina-Franco, MD, Ruben Cortes, MD, Lorenzo de la Garza, MD, and Armando Gamboa-Dominguez, MD

From the Service of Colon and Rectal Surgery and the Service of General Surgery, Department of Surgery, and the Department of Pathology, Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran, Mexico City, Mexico.

Reprint requests to Takeshi Takahashi, MD, FACS, Department of Surgery, Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran, Vasco de Quiroga 15, Delegacion Tlalpan, Mexico City 14000, Mexico. Email: [e-mail]