Anorectal melanoma is a malignant tumor that develops from melanocytes and is localized in the lower ampullary rectum or in various areas of the anorectal zone. It is manifested by bleeding, pain, foreign body sensation in the anus, constipation, tenesmus and anal itching. It is prone to early lymphogenic and hematogenic metastasis, the first clinical sign may be dysfunction of various organs due to metastasis. The diagnosis is established on the basis of complaints, anamnesis, general and rectal examination data, examination of smear prints and other studies. The treatment is operative.
ICD 10
C20 C21
General information
Anorectal melanoma is a malignant melanocytic tumor located in the lower parts of the rectum or the anus. It is 2-3% of the total number of melanomas and 0.25-1.8% of the total number of malignant neoplasms of the rectum. It is detected in different age groups, the average age of patients is 45 years. It affects men and women equally often. Like other malignant tumors originating from melanocytes, it is characterized by rapid progression and metastasis.
Due to the external similarity with other diseases, the frequent absence of pigment or insufficient pigmentation, melanoma of the anorectal area may be misdiagnosed, which further worsens the prognosis. The frequency of diagnostic errors during the initial treatment reaches 35%. Patients can receive treatment for rectal polyps, hemorrhoids, anal fissure, paraproctitis, rectal cancer and other diseases. In some cases, there are no clinical manifestations, the tumor is detected during an examination for another reason. The treatment is carried out by specialists in the field of clinical oncology and proctology.
Pathological anatomy
Melanoma of the anorectal region can occur in the ampullary rectum, the anal canal area or (less often) the ampullary ring. It usually grows exophytically, in appearance resembles a hemorrhoid node or a polyp on a narrow leg or a wide base. Less often, endophytic growth with the formation of ulcerated infiltrates is observed. Sometimes there are saucer-shaped melanomas of the anorectal region surrounded by a clearly defined roller, outwardly similar to carcinomas. The size of the neoplasm can range from 1 to 8 cm. In 20% of cases, multiple tumors are detected. The color of melanoma can be black, dark brown, cherry or burgundy. There are “variegated” neoplasms with alternating pigmented and non-pigmented zones. In 50% of cases, melanomas of the anorectal region are devoid of pigmentation.
Taking into account the features of the histological structure, four types of tumors are distinguished: epithelial, fusiform, round-cell and polymorphocellular. When examining epithelial-like melanomas of the anorectal region, solid nests are revealed, around which argyrophilic membranes are located. When studying spindle-cell neoplasms, individual braiding of cells is detected. Round-cell tumors are characterized by single round cells of small size, argyrophilic fibers are absent. “Pure” neoplasms are rare, in most anorectal melanomas consist of tissue sections with different structures.
Symptoms
In most cases (more than 80%), the first symptom of anorectal melanoma is an admixture of blood in the feces. Due to the low location of the tumor, hemoglobin does not have time to turn into hydrochloric acid hematin, so the blood remains bright scarlet, clearly visible on the surface of the stool. More than half of the patients complain of pain in the anus. Among the less common manifestations of anorectal melanoma are a feeling of a foreign body, tenesmus, a feeling of incomplete bowel emptying, constipation and itching in the anus. Some patients report the presence of a tumor-like formation in the anus. Sometimes melanoma falls out of the rectum during defecation, and patients set it with their hand.
A large number of blood and lymphatic vessels are located in the rectum area, which causes the tendency of anorectal melanoma to early metastasis. At the time of initial treatment, metastases are detected in almost 20% of patients, and subsequently occur in more than half of patients. Melanoma of the anorectal region usually metastasizes to the inguinal lymph nodes, bones, lungs, liver and skin. Sometimes metastases or related disorders of the function of internal organs become the first clinical manifestation of the disease. Pronounced infiltrative growth with damage to neighboring organs is observed less often. Melanoma can germinate the labia majora, vagina, scrotum root, pelvic walls, etc.
Diagnostics
The diagnosis of anorectal melanoma is established taking into account complaints, anamnesis, the results of a general examination, rectal examination and smear-fingerprint examination. Rectal examination is carried out very carefully, without using mirrors. Conducting a biopsy if this pathology is suspected is contraindicated. In doubtful cases, an express biopsy is indicated during surgical removal of a malignant neoplasm. To detect metastases, patients are referred for chest x-ray, bone x-ray and scintigraphy, liver ultrasound and other studies.
Melanoma of the anorectal region is differentiated with a thrombosed hemorrhoid node, benign and malignated adenomatous polyp, rectal cancer, lymphosarcoma, carcinoid and malignant schwannoma. Due to the lack of specific symptoms, the external similarity of anorectal melanoma with other neoplasms and the frequent absence of pigmentation, differential diagnosis based on clinical signs causes significant difficulties. The main method is smear-fingerprint microscopy. Special methods of staining samples are used to detect promelanin. Pay attention to the presence of signs of appositional growth at the edges of the neoplasm.
Treatment
The main method of treatment of anorectal melanoma is surgical intervention. If possible, abdominal anal extirpation of the rectum is carried out. In case of metastasis to the inguinal lymph nodes, their removal is performed. Palliative surgery is ineffective and even in combination with other methods (chemotherapy, radiotherapy) they do not significantly affect the life expectancy of patients.
Prognosis and prevention
Due to the asymptomatic or low-symptomatic course, late access to an oncologist and the difficulties of diagnosis, treatment of anorectal melanomas usually begins when the tumor has already reached a significant size and has penetrated deep into the underlying tissues. Melanomas of any localization detected at this stage are characterized by an extremely unfavorable course. According to American oncologists, currently the average five-year survival rate for anorectal melanoma ranges from 12 to 22%.