eP415 - Misplaced Mammary Gland: A Case Report on Ectopic Mammary Tissue in the Peri-anal Region

Purpose/Background: Ectopic mammary tissue is rare, particularly in the peri-anal location. More common locations of ectopic breast tissue are axillae, vulva, neck, and groin (1). Accessory breast tissue is thought to occur due to involutional failure of the mammary ridge, also known as the embryonic milk line, at two to three months’ gestation. This line extends bilaterally from the axillae to the proximal inner thighs. The spectrum of extra-mammary breast tissue lesions along the milk ridge ranges from rudimentary lumps to fully formed nipple-areola complexes (2). Histology can vary widely in the context of peri-anal mammary lesions including but not limited to fibroadenomas, Paget’s disease, lobular intraductal and phyllodes tumors (3). Though symptoms differ based on the underlying histopathology, the majority of these mammary-like perianal lesions are found incidentally on physical examination. We present a case of symptomatic extra-mammary peri-anal lesion.

A 37-year-old female with past medical history of constipation presented to clinic with a new slowly growing peri-anal skin tag with associated bright red blood per rectum. She denied any family history of colon or rectal cancers. Her anal-rectal examination and proctoscopy was significant for a 2cm friable, non-tender lesion in the left perianal region without associated external or enlarged internal hemorrhoids. Human papilloma virus (HPV) vaccination status was unknown. Her Papanicolaou smear test two years prior was unremarkable, and she had never undergone colonoscopy. She denied any tenesmus, vaginal bleeding, weight loss, anorexia, or family history of colon cancer.Methods/Interventions: The peri-anal lesion, measuring 1.7x1.0x0.4 cm, was removed with wide local excision in the clinic. Pathology confirmed the lesion was comprised of benign heterotopic mammary-like glands with overlying reactive squamous epithelium. These findings resembled a nipple duct adenoma arising from ectopic breast tissue. P16 staining was negative with positive estrogen and progesterone receptors (ER, PR positive). The overlying squamous epithelium was hyperkeratotic without evidence of condyloma.Results/Outcomes: Given the hormonal activity of the lesion, she underwent further wide local excision to ensure negative margins for prevention of recurrence. The patient decided against additional intervention but was agreeable to routine follow-up.Conclusion/

Discussion: Ultimately, while peri-anal mammary tissue is rare, this case confirms the necessity of a broad differential when assessing anal lesions with consideration for hemorrhoids, perianal abscess, endometriosis, primary anorectal tumors and mammary-like glandular lesions. Given the breadth of differentials associated with peri-anal lesions, it is imperative to complete a thorough work-up with biopsy or excision of the lesion and detailed pathology assessment.