A 57–year–old Caucasian female started having painless bleeding per rectum. She denied any constipation or pain during bowel movements. She noticed small lump at anal margin. Her other co–morbidities were hypertension, hyperlipidemia, stress incontinence and lumbar degenerative disc disease. She did not have any family history of cancer. Sigmoidoscopy at PCP’s office showed mass in anal canal which was diagnosed as hemorrhoids. Hemorrhoidectomy was suggested but was delayed due to inability to lie down for procedure due to exacerbation of spinal degenerative disc disease. The mass gradually increased in size over months and she continued to bleed. She was referred to a surgeon who noted a yellowish tan colored, ulcerated mass of tennis ball size .It was thought to be grade 4 hemorrhoid. Hemorrhoidectomy was performed and specimen was sent for routine pathology. Pathology report showed epitheloid cells with nuclear polymorphism and brisk mitotic activity. IHC staining was positive for S–100 and HMB 45. IHC and morphology in combination confirmed diagnosis of invasive malignant melanoma with fibro muscular infiltration. PET scan showed primary lesion in rectum with multiple liver lesions. Mild hyper metabolism was noted even in mediastinal nodes. Stage IV metastatic melanoma was diagnosed and subsequent workup with MRI of brain and bone scan were negative. MUGA and PFT’s were normal. She was admitted for biological therapy with high dose Interleukin–2 and is being considered for targeted therapy including enrollment in an anti–CTLA 4 (Ipilimumab) trial.
Malignant melanoma commonly occurs in sun exposed areas, especially in pre existing moles. It also occurs in other forms like ocular, ungual, plantar and palmar. Mucosal forms occur in head, neck, vulva, vagina and anorectal areas. Most of anorectal melanomas are metastases from cutaneous primary. Primary anorectal melanomas account for 0.05% of all tumors that occur in colorectal region. They are typically an incidental finding on routine pathology. They usually present with pain, pruritis, bleeding or prolapse. It sometimes disguise as hemorrhoids. Distant metastases are found about 30% of the time at diagnosis. It usually carries poor prognosis. This case illustrates an example of unfamiliarity with this tumor leading to development of stage IV disease.
Malignant tumors like melanoma should be considered in differential of prolapsing or bleeding masses in addition to common causes like hemorrhoids. Biopsy of all anorectal masses seen on exam is imperative, irrespective of successive surgery in order to avoid delay in diagnosis of rare but malignant tumors like melanoma.