Introduction

Mammary-type tissues or ectopic breast tissue of the labia majora are clinically significant, though rare, and likely arise from disrupted embryological, hormonal, and histological develop­ment. Since 1872, fewer than 40 cases of congenital, ectopic mam­mary tissues in the labia majora have been studied [1]. Many of these tissues exhibit functional and morphological similarity to orthotopic mammary glands, undergoing comparable physiolog­ical and pathological transformations. Their existence highlights developmental remnants of the mammary ridge, also known as the ‘milk line’, a ridge of ectoderm that extends from the axilla to the groin [2,3].

Ectopic mammary-like glands, particularly within the interla­bial sulcus between the labia majora and minora, may often re­main asymptomatic. Physiological changes during pregnancy or lactation often bring them to clinical attention [3]. They become

clinically apparent due to hypertrophic, secretory, and sometimes pathological changes under reproductive hormone influence in the ante- and postpartum period [3].

Ectopic mammary-like gland proliferation in the vulva is histologically heterogeneous, varying from simple tubular duct structures to more complex lobular arrangements reminiscent of mammary tissue [4,5]. Classification can be supported immuno­histochemically using markers such as GCDFP-15 [4]. These struc­tures are thought to arise from embryonic precursors of the milk line, although some propose an apocrine origin, as they may ex­hibit morphological, hormonal, and neoplastic features analogous to those of mammary gland tissue. Their specific developmental origin, however, remains unclear [6]. Clinical presentations of such tumors warrant serial histopathological and radiological as­sessments [2,3,7] for accurate diagnosis.

Mammary-type tissues or ectopic breast tissue of the labia majora are clinically significant, though rare, and likely arise from disrupted embryological, hormonal, and histological develop­ment. Since 1872, fewer than 40 cases of congenital, ectopic mam­mary tissues in the labia majora have been studied [1]. Many of these tissues exhibit functional and morphological similarity to orthotopic mammary glands, undergoing comparable physiolog­ical and pathological transformations. Their existence highlights developmental remnants of the mammary ridge, also known as the ‘milk line’, a ridge of ectoderm that extends from the axilla to the groin [2,3].

Ectopic mammary-like glands, particularly within the interla­bial sulcus between the labia majora and minora, may often re­main asymptomatic. Physiological changes during pregnancy or lactation often bring them to clinical attention [3]. They become

clinically apparent due to hypertrophic, secretory, and sometimes pathological changes under reproductive hormone influence in the ante- and postpartum period [3].

Ectopic mammary-like gland proliferation in the vulva is histologically heterogeneous, varying from simple tubular duct structures to more complex lobular arrangements reminiscent of mammary tissue [4,5]. Classification can be supported immuno­histochemically using markers such as GCDFP-15 [4]. These struc­tures are thought to arise from embryonic precursors of the milk line, although some propose an apocrine origin, as they may ex­hibit morphological, hormonal, and neoplastic features analogous to those of mammary gland tissue. Their specific developmental origin, however, remains unclear [6]. Clinical presentations of such tumors warrant serial histopathological and radiological as­sessments [2,3,7] for accurate diagnosis.

Case Report

We highlight the case of a 20-year-old woman presenting with a large vulval mass identified antenatally, which resolved in the postpartum period. She was known to have a chromosomal du­plication (1q34q44) and had been socially isolated, living inde­pendently with disability support. Her history was notable for in­tellectual disability, speech impediment, dyslexia, and gestational thrombocytopenia.

She received shared antenatal care through Mildura Base Hos­pital and was referred at 36 weeks for review of a newly diagnosed vulval mass. Initially appearing small and insignificant, it grew by 38 weeks to nearly 10cm. She remained asymptomatic. Perineal ultrasound demonstrated an irregular, predominantly firm mass with increased vascularity, anterior to the anal opening. It was considered unlikely to be a Bartholin’s cyst or a drainable abscess. Given its growth and the risk of complication during vaginal deliv­ery, a collaborative decision was made for elective lower uterine segment delivery at 39 weeks, combined with diagnostic surgical evaluation.

At Caesarian section, she delivered a live female infant of 3590g (60^th percentile) with an estimated blood loss of 750ml. The right labial mass was approximately 8-10cm in diameter, firm and non-fluctuant, without apparent fluid content. Vaginal and rectal mucosa appeared normal and were not tethered or conflu­ent with the mass. A small incisional biopsy was performed by the general surgical team, with formal resection deferred pending his­topathology.

Postoperatively, tumor markers showed elevated CA-125 (77U/ml) and normal CEA (0.9U/mL) and CA 19-9 (5U/mL). Pel­vic MRI of the pelvis demonstrated a 6.7cm well-defined mixed solid-cystic mass arising from the posterior aspect of the right labia majora, inconsistent with a labial hematoma and without in­guinal lymphadenopathy. A contrast-enhanced MRI was declined to allow breastfeeding.

Histopathology reported a “dermoid proliferation of naevoid cells with nests and cords of bland epithelioid cells without sig­nificant mitotic activity, with marked maturation with depth and no evidence of malignancy”. Notable were proliferated glands lined with vacuolated epithelial cells surrounded by myoepithelial cells and larger ductular structures lacking mitotic activity. Im­munochemistry was positive for cytokeratins AE1/AE3, and tran­scription factor GATA3 (commonly expressed in breast epitheli­um and urothelium), alongside p63 and SOX10 staining typical of myoepithelial cells. This confirmed benign mammary-type tissue with lactational changes.

The core biopsy site later became infected, associated with erythema and drainage of pus. Swabs grew enteric flora and Pseu­domonas aeruginosa; treatment involved removal of sutures and wound care.

The patient was referred to the Royal Women’s Hospital in Melbourne for further evaluation by gynecological oncologists. She chose to stop breastfeeding, and further assessment was planned after lactational involution. Psychological support and ongoing monitoring were arranged. At last contact, the mass had resolved and was no longer palpable.

Discussion

The labia majora, a functionally dynamic part of the external genitalia, responds to physiological stimuli such as age, hormonal fluctuations, and parity. In reproductive periods, particularly lac­tation, hypertrophy and hypervascularisation of mammary-type tissue can occur in response to prolactin and oxytocin [3,8].

Mammary-like tissue masses in the labia majora may present as asymptomatic nodules or cause pain and progressive enlarge­ment, typically during pregnancy or lactation. Although general­ly benign, they may undergo changes resembling those seen in hidradenoma papilliferum, Bartholin’s cysts, or other neoplastic disorders of the vulva [8]. Published literature reports the special­isation of these tumors, typical of breast tissues, including fibro­adenomas [9], as well as neoplastic transformations into ductal carcinomas and adenoid cystic carcinomas [4,10-12].

A comparable case study by Sharma et al. [13] describes a 24-year-old primigravid woman with a vulval mass at 14 weeks identified as a lactating adenoma. They noted an incidence of ec­topic breast tissue of 2-6%, often diagnosed during pregnancy as labial enlargement. Complete excision is recommended to reduce recurrence and mitigate malignant risk, supported by broader lit­erature on the neoplastic transformations of these tissues [14]. Thus, symptomatic or enlarging lesions require excisional biopsy and interdisciplinary management involving gynecologists, pa­thologists, and oncologists [3,9].

This case underscores the importance of considering ectopic, mammary-like tissue in the differential diagnosis of vulvar mass­es, especially during pregnancy. Prompt recognition helps avoid misdiagnosis, enables appropriate interdisciplinary planning, and ultimately supports safer maternal and neonatal outcomes. Immu­nohistochemistry remains a cornerstone for differentiating mam­mary-type tumors from other vulvar neoplasms employing mark­ers such as cytokertins, estrogen, and progesterone receptors [2]. Notably, positivity for both cytokertins and GATA3, as observed in our case and others [15], highlights the breast-like differentiation of these tissues [16,17].

Conclusion

Mammary-type tissues in the labia majora, though rare, repre­sent a clinically significant anatomical variant. Their dynamic re­sponsiveness to hormonal stimuli, potential for neoplastic change, and implications for vulvar health highlight the importance of multidisciplinary care. In our case, additional complexities includ­ed multidisciplinary planning to support informed decision-mak­ing and postpartum care, given the patient’s intellectual disability and social circumstances. Future research focusing on genetic and molecular profiling may help refine diagnostic criteria and clinical management and shed light on whether chromosomal anomalies may influence ectopic mammary tissue development.

References

1. Larson S, Yang S, Chacko-Stacey A, Mason D, Hart E (2019) Self-resolving vulvar breast tissue arising in the postpartum setting: a case report and review of literature. Journal of Human Lactation 36(2): 348-351.
2. Amălinei C, Giuşcă SE, Căruntu ID (2015) Fibroadenomas of anogenital mammary-like glands: from embryogenesis anomaly to apocrine origin. Polish Journal of Pathology 66(3): 219-223.
3. Mikhael S, Nilsson W, Patel K, Graf S (2017) Ectopic breast tissue of the vulva in a postmenopausal woman. Case Reports in Obstetrics and Gynecology 2017: 1-2.
4. Butler B, Leath CA, Barnett JC (2014) Primary invasive breast carcinoma arising in mammary-like glands of the vulva managed with excision and sentinel lymph node biopsy. Gynecologic Oncology Case Reports 7: 7-9.
5. Nishie W, Sawamura D, Mayuzumi M, Takahashi S, Shimizu H (2004) Hidradenoma papilliferum with mixed histopathologic features of syringocystadenoma papilliferum and anogenital mammary‐like glands. Journal of Cutaneous Pathology 31(8): 561-564.
6. Willman J, Golitz L, Fitzpatrick J (2005) Vulvar clear cells of Toker: precursors of extramammary Paget's disease. American Journal of Dermatopathology 27(3): 185-188.
7. Sington J, Manek S, Hollowood K (2002) Fibroadenoma of the mammary‐like glands of the vulva. Histopathology 41(6): 563-565.
8. Moore KG, Miedema JR, Corley SB (2025) Recurring papules and nodules on the vulva. JAMA Dermatology 161(5): 549-550.
9. Berwal A, Kancharla K (2025) Exploring vulval fibroadenoma: a rare entity. Cureus 17(2): e78714.
10. Torky H, Elshenawy A, Eesa A (2017) Infiltrating mammary duct adenocarcinoma in the right labia majora along the milk line. Zeitschrift Für Geburtshilfe Und Neonatologie 221(06): 283-285.
11. Wang W, Chen H, Guo H, Chen L, Zhu M, et al. (2022) Adenoid cystic carcinoma of the Bartholin’s gland is easily misdiagnosed: a case report and literature review. Medicine 101(45): e31744.
12. León DC, Pérez‐Montiel D, Vázquez H, Jimenez C, Cetina L, et al. (2009) Vulvar fibroadenoma: a common neoplasm in an uncommon site. World Journal of Surgical Oncology 7(1): 70.
13. Sharma A, Sharma M, Sharma V, Khajuria A, Mahajan S (2013) Lactating adenoma of ectopic breast tissue in the vulvar region. Indian Journal of Basic and Applied Medical Research 3(1): 212-214.
14. Wilkinson EJ, Massoll NA (2011) Benign diseases of the vulva. In: RJ Kurman, ML Carcangiu, C Herrington, RH Young (Eds.), Blaustein’s pathology of the female genital tract. (6^th edn), Springer, pp. 1-53.
15. Arora K, El-Zaatari ZM, Schwartz MR, Ro JY (2020) Lesions of anogenital mammary-like glands: four cases including novel pathologic and immunohistochemical observations. Annals of Diagnostic Pathology 47: 151551.
16. Baker GM, Selim MA, Hoang MP (2013) Vulvar adnexal lesions: a 32-year, single-institution review from Massachusetts General Hospital. Archives of Pathology & Laboratory Medicine 137(9): 1237-1246.
17. Pieh-Holder K (2013) Lactational ectopic breast tissue of the vulva: case report and brief historical review. Breastfeeding Medicine 8(2): 223-225.