Challenges in managing anorectal melanoma, a rare malignancy

Abstract

Introduction and importance

Anorectal melanoma is a rare and aggressive malignancy that can be difficult to diagnose due to its nonspecific presentation.

Case presentation

We present a case of a 69-year-old woman who presented with painful defecation, bleeding per rectum, and a mass coming out of her anal opening. The initial differential diagnosis included hemorrhoids, rectal polyp, or a malignant lesion of the rectum. However, histopathological evaluation following transanal excision of the rectal mass revealed mucosal melanoma in the anorectal region. Further investigation showed no evidence of locoregional or distant metastasis.

Clinical discussion

Surgery remains the primary treatment option for anorectal melanoma, but complete resection is often not feasible, leading to high rates of local recurrence and distant metastasis. The incidence of metastatic disease at the time of presentation is high, and a multidisciplinary approach is necessary to manage these patients. Currently, standard systemic therapies used for cutaneous melanoma are the mainstay of treatment for metastatic anorectal melanoma, but there is a need for further research to develop tailored treatment strategies.

Conclusion

Our case report highlights the importance of considering anorectal melanoma in the differential diagnosis of patients presenting with anorectal symptoms. It emphasizes the need for a multidisciplinary approach to managing this rare malignancy. Early diagnosis, a multidisciplinary approach, and ongoing research into more effective treatments are crucial for improving outcomes for patients with anorectal melanoma.

Highlights

• •Anorectal melanoma is a rare and aggressive malignancy.
• •It can be difficult to diagnose due to its nonspecific presentation.
• •It should be considered as a differential diagnosis for patients presenting with anorectal symptoms.
• •Surgery remains the primary treatment option.

1. Introduction

Anorectal melanoma is a rare type of cancer that develops in the cells that produce pigment in the anus or rectum. Melanoma can develop in any part of the body that contains pigment cells, including the skin, eyes, and the lining of internal organs. Anorectal malignant melanoma exhibits submucosal plane metastasis [1], rendering it frequently unresectable upon initial diagnosis. Its etiology remains unknown, with surgical intervention serving as the cornerstone of management. However, the diagnosis of anorectal melanoma can be challenging, as it initially follows the typical diagnostic pathway for anorectal masses. Additionally, clinical misdiagnosis has been reported in nearly 60 % of cases [2]. At the time of presentation, over 70 % of patients may have metastatic disease. The management of metastatic anorectal melanoma is based on standard systemic therapy for metastatic (cutaneous) melanoma, and there is a paucity of data on the management of metastatic anorectal malignant melanoma [3]. As a result of the rarity and the consequent paucity of literature data about efficient therapeutic strategies, this melanoma subtype is characterized by a worse prognosis than melanoma arising from the skin. In this article, we summarize the current state of knowledge regarding anorectal melanoma as a model of rare melanomas deserving of a multidisciplinary approach, with the involvement of experts in the field of urogenital and anorectal malignancies. We also highlight the challenges in managing anorectal melanoma and the need for further research to develop tailored treatment strategies. This article was written according to the SCARE guidelines [4].

2. Presentation of case

A 69-year-old lady presented with painful defecation, bleeding per rectum, and a mass coming out of her anal opening. The symptoms had been present for the past year. She also reported a weight loss of 10 kg over the same period. She denied any altered bowel habits, abdominal pain, or jaundice. On physical examination, the patient appeared pale. Per rectal examination revealed a hard mass in the posterior wall of the rectum coming out of the anal verge. The resting and squeeze anal tones were normal. There was no clinical evidence of inguinal lymphadenopathy. Based on the patient's symptoms and examination findings, the differential diagnosis included hemorrhoids, rectal polyp, malignant lesion of the rectum.

Laboratory investigations revealed low haemoglobin level and elevated alkaline phosphatase. The rest of the parameters were within normal limits. Colonoscopy revealed a pedunculated mass at the 4 o'clock position in the lower rectum involving the anorectal junction (Fig. 1). Colonoscopic biopsy was taken which was inconclusive of a malignant lesion. Abdomino-pelvic contrast-enhanced computed tomography didn't show any evidence of locoregional or distant metastasis.

Fig. 1.

Colonoscopy showing a pedunculated mass in the lower rectum.

The patient underwent a transanal excision of the rectal mass. There was no involvement of the anal sphincter. The resected specimen was sent for histopathological evaluation which showed a microscopic tumour-free margin along with haphazardly arranged large pleomorphic cells with prominent nucleoli. Both intracellular and extracellular coarse black non refractile melanin pigment present (Fig. 2) with a satisfying bleaching effect. Immunohistochemistry revealed that the specimen was positive for HMB-45 and S-100 suggestive of mucosal melanoma in the anorectal region. The postoperative period was uneventful and the patient was discharged on postoperative day 4. She was advised adjuvant chemotherapy, however, was not keen on going down that line. Follow-up PET-CT was done after 1st month and 6th month which did not show any evidence of recurrence. She was symptom-free with no clinical evidence of recurrence on a 16-month follow-up.

Fig. 2.

Histopathology image showing polygonal cells with melanin pigment.

3. Discussion

Anorectal melanoma is a rare but aggressive malignancy that poses a significant challenge to clinicians due to its nonspecific presentation [5] and often-delayed diagnosis [6]. Our case report highlights the importance of including anorectal melanoma in the differential diagnosis of patients presenting with symptoms such as painful defecation, bleeding per rectum, and an anal mass [7]. The clinical presentation of anorectal melanoma is similar to other more common anorectal pathologies, such as hemorrhoids and rectal polyps, leading to delayed diagnosis in a significant number of cases [8].

It is often invisible and lacks pigmentation, making it difficult to diagnose, especially in cases where the tumours are amelanotic. Patients usually present with symptoms such as bleeding, discoloration of the skin, changes in bowel habits, anorectal pain or discomfort, and hemorrhoids. The incidence of anorectal melanoma is low, accounting for less than 1 % of all cases of melanoma and less than 4 % of all anorectal cancers. However, it has a high mortality rate, with a five-year survival rate of less than 10 % [5].

These tumours mainly affect women, with a mean age of 68 years [9]^, [10]^, [11]. It is often diagnosed late in its course due to its nonspecific presentation, which is similar to that of other common anorectal disorders such as hemorrhoids. The initial management of anorectal malignant melanoma involves biopsy of the mass through colonoscopy or proctoscopy. The differential diagnosis includes Paget's disease, Bowen's disease, lymphoma, and gastrointestinal stromal tumour. Further, careful pathologic evaluation is necessary for clinical staging, especially in cases where the tumours are amelanotic, and tumour mutation panels are required.

These can develop in the proximity of, at, or distant from the anal border. When it arises close to the anal verge, it is considered an anal melanoma. Regardless of the location of the disease, its presentation is similar. Per rectal bleeding is the most common symptom, reported in up to 55 % of patients [12]. Other presentations may include rectal pain, changes in bowel habits, and pruritus. These cases are frequently misdiagnosed as hemorrhoids due to the similarity in presentation. Typically, patients experience symptoms for 4–6 months before being correctly diagnosed [13].

The melanin stain and immunohistochemistry are used to establish a diagnosis by detecting positive staining for melanocyte markers, including S100, HMB-45, and Vimentin [13]. Mutation analysis is also recommended for all melanoma patients, with a negative BRAF V600 mutation analysis being indicative of a mucosal melanoma [14].

Surgery is the primary treatment option for anorectal malignant melanoma. Local excision and abdominoperineal resection are usually the preferred surgical options, although the extent of resection depends on the stage of the disease. Radiation therapy, chemotherapy, and immunotherapy are also used in the management of anorectal malignant melanoma. The response rate in patients with mucosal melanoma receiving nivolumab was 53 %, while combination therapy with nivolumab and ipilimumab can improve response rates up to 60 % but has more toxicity [14].

Patients are at high risk of developing local recurrence and distant metastasis, with the most common metastasis sites being the lung and liver. Therefore, computed tomography and ultrasonography are essential for staging and follow-up in assessing regional disease and recurrence [15].

Metastatic disease is associated with a poor prognosis, and there is a lack of data on effective systemic therapies for this rare subtype of melanoma. Currently, standard systemic therapies used for cutaneous melanoma are the mainstay of treatment for metastatic anorectal melanoma. However, there is a need for further research to develop tailored treatment strategies for this malignancy.

Our case report demonstrates the importance of considering anorectal melanoma in the differential diagnosis of patients presenting with anorectal symptoms. In addition, it emphasizes the need for a multidisciplinary approach to managing this rare malignancy, involving experts in the field of urogenital and anorectal malignancies. With the limited data available on effective treatment strategies for anorectal melanoma, further research is required to develop tailored approaches for this aggressive malignancy.

4. Conclusion

In conclusion, anorectal melanoma is a rare and aggressive malignancy that poses a significant challenge to clinicians due to its nonspecific presentation and often-delayed diagnosis. Delayed diagnosis can result in more extensive surgeries, delayed treatment, and a poor prognosis. Surgery remains the primary treatment option, but the complete resection is often not feasible, leading to high rates of local recurrence and distant metastasis. The incidence of metastatic disease at the time of presentation is high, and the management of metastatic anorectal melanoma requires a multidisciplinary approach involving experts in the field of urogenital and anorectal malignancies. Currently, there is a lack of data on effective systemic therapies for this rare subtype of melanoma. Further research is required to develop tailored treatment strategies for this malignancy. Early diagnosis, a multidisciplinary approach, and ongoing research into more effective treatments are crucial for improving outcomes for patients with anorectal melanoma.

Consent

Written informed consent was obtained from the patient for the publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal on request.

Provenance and peer review

Not commissioned, externally peer-reviewed.

Ethical approval

Not required in our institution to publish anonymous case reports.

Funding

Nil.

Author contribution

Jyotirmoy Biswas: Acquisition of the data, drafting the manuscript, final approval of the version to be submitted.

Lakshmi Deepak Bethineedi: Acquisition of the data, drafting the manuscript, final approval of the version to be submitted.

Arkadeep Dhali: Conception, design of the study, acquisition of the data, drafting the manuscript, final approval of the version to be submitted.

Jamal Miah: Revision of manuscript, final approval of the version to be submitted.

Sukanta Ray: Conception, design of the study, acquisition of the data, drafting the manuscript, final approval of the version to be submitted.

Gopal Krishna Dhali: Acquisition of the data, final approval of the version to be submitted.

Guarantor

Prof. Gopal Krishna Dhali will act as guarantor of the article.

Research registration number

Not applicable.

Conflict of interest statement

None.