Granulomatous lobular mastitis involving accessory breast tissue: a case report and review of the literature

A 32-year-old woman with granulomatous lobular mastitis, or GLM, involving accessory breast tissue in her left axilla experienced progressive pain, swelling and ulceration despite several courses of antibiotics and other treatments, according to a case report published in Frontiers in Oncology. The report combined the woman’s clinical course with a narrative review that identified only five previously published cases of the condition, highlighting how rarely GLM has been documented in accessory breast tissue. This single-patient report and non-systematic literature synthesis cannot establish a standard diagnostic or treatment protocol, but it documents a rare presentation, its histological features and one patient’s clinical course after surgical excision and reconstruction.

The woman initially noticed a painful mass beneath the skin of her left armpit without an obvious trigger. Over two months, it enlarged to approximately egg size and developed redness, warmth and tenderness. One week of intravenous levofloxacin and ofloxacin at another hospital did not produce clear improvement. Intermittent intravenous anti-inflammatory treatment of unspecified type, repeated local injections of gentamicin sulfate and triamcinolone acetonide acetate, and intermittent cephalosporin antibiotics provided only partial or temporary relief, while axillary pain continued to worsen. She had previously undergone bilateral axillary fibroma excision and removal of a right accessory nipple, and she had two cesarean deliveries, five years and one year before presentation. She had breastfed after both pregnancies but denied taking oral contraceptives.

Examination at Dongzhimen Hospital of Beijing University of Chinese Medicine found an indurated mass approximately 8.0 by 6.0 cm beneath an old 10-cm surgical scar in the left axilla. Its margins were ill defined, and the surrounding area was swollen, erythematous, tender and warm. Two small ulcers, each about 0.3 cm, above the scar released yellow purulent material. Several ipsilateral axillary lymph nodes were enlarged, with the largest measuring about 1.0 by 1.0 cm, while no enlarged supraclavicular or infraclavicular nodes were detected. The breasts themselves were symmetrical, without a palpable mass, nipple-areolar deformity or peau d’orange change. Her vital signs were stable, and she had no fever, arthralgia or other systemic symptoms identified during the clinical evaluation.

Ultrasound detected accessory-gland tissue in both axillae. On the right, a 1.1 by 0.5 cm mixed-echogenic nodule within the accessory tissue was assigned BI-RADS category 3. On the left, multiple patchy mixed-echogenic lesions, the largest measuring 4.1 by 3.4 by 1.0 cm, had indistinct margins, scattered punctate hyperechoic foci and abundant surrounding blood flow. The radiologists interpreted the left-sided findings as an inflammatory lesion with abscess formation, and mild enlargement of the left axillary lymph nodes was also observed. Based on the clinical manifestations, examination and ultrasound, the treating team considered GLM involving the left accessory breast tissue to be the most likely diagnosis and recommended surgery.

The operation included removal of accessory breast tissue on both sides, together with local skin-flap transfer and reconstruction. Multiple abscess cavities filled with inflammatory necrotic granulation tissue were found in the left axilla, and yellowish, caseous, lipid-like material emerged from ducts under gentle compression, indicating extensive inflammatory involvement of the left accessory tissue. The affected tissue was fully excised, the operative field was irrigated and drained, and a lateral thoracic adipofascial flap was used to repair the defect and restore contour. The right-side tissue was removed at the patient’s request after ultrasound had categorized its small nodule as BI-RADS 3. The authors explicitly described that decision as individualized rather than evidence based, noting that the available evidence does not support routine prophylactic removal of unaffected accessory tissue on the opposite side.

Histopathological examination confirmed GLM with duct ectasia in the left specimen, whereas the right specimen showed isolated duct ectasia without GLM. GLM is a benign chronic inflammatory disease characterized by granulomatous inflammation centered on the terminal duct lobular units of the breast. Its characteristic microscopic features include non-caseating granulomas formed by epithelioid histiocytes and multinucleated giant cells, often with lipid-containing central vacuoles, suppurative inflammation and varying degrees of fat necrosis. The report identifies histopathological examination as the diagnostic gold standard because the condition’s clinical and imaging appearances are nonspecific and can overlap with inflammatory breast carcinoma and periductal mastitis.

Accessory breast tissue is a congenital developmental anomaly caused by incomplete regression of the embryonic mammary ridge. It occurs in an estimated 2% to 6% of women and is most often found in the axilla, although it can develop elsewhere along the embryonic milk line, including the chest wall, abdomen, face, neck and upper limbs. The tissue can contain mammary glands, a nipple, an areola or combinations of these structures, a system described by the Kajava classification. In the reported case, glandular tissue remained in both axillae after a right accessory nipple had been removed 13 years earlier. Because accessory glands share the basic histological characteristics of breast tissue, they may also respond to endocrine changes associated with menstruation, pregnancy and lactation. The authors noted that accessory breast tissue can undergo both benign and malignant pathological changes, but GLM affecting it has rarely been documented.

The authors’ narrative search covered PubMed, Web of Science, Embase, CNKI and Wanfang Data from database inception through March 1, 2026. English- and Chinese-language reports were eligible when histopathology confirmed granulomatous lobular mastitis arising in accessory or ectopic breast tissue. Only five cases were identified, and the authors emphasized that the review was narrative rather than systematic, so exhaustive retrieval could not be guaranteed. Across the small body of published cases, patients were generally parous women with a history of breastfeeding, sometimes within three to five years after childbirth. Reported lesions were painful, firm or board-like masses with poorly defined borders; erythema, swelling, abscess formation, purulent ulceration and regional lymphadenopathy occurred in some cases. The authors also observed that accessory nipples were frequent in the reported cases and proposed that incompletely developed duct systems might promote retained secretions and ductal dilatation, while describing this as a hypothesis rather than a demonstrated causal mechanism.

Ultrasound is the principal imaging method for assessing these lesions and mapping their extent, although its findings are not specific. GLM may appear as an irregular hypoechoic or mixed lesion with indistinct margins, ductal dilatation, increased vascularity and abscess formation. Distinguishing it from inflammatory breast cancer is particularly important because both can cause erythema, edema, tenderness and a palpable mass. Histology showing malignant cells would establish cancer, whereas GLM produces lobule-centered granulomatous inflammation. Periductal mastitis can resemble GLM as well, but it generally centers on the nipple-areolar region and shows ductal dilatation with dense periductal lymphocytes and plasma cells rather than lobular granulomas. The authors also list IgG4-related mastitis, tuberculous mastitis, fat necrosis and foreign-body granuloma among possible differential diagnoses.

No consensus currently defines the optimal treatment for GLM involving accessory breast tissue. Available approaches include corticosteroids, antibiotics aimed at possible lipophilic organisms, other immunosuppressive drugs, traditional Chinese medicine, incision and drainage, and excision of involved tissue. Trimethoprim, clindamycin, methotrexate, azioprine and cyclosporine A have been used in reports of GLM, but medical treatment can produce adverse effects such as Cushing syndrome, weight gain and hyperglycemia. Evidence specific to accessory-breast disease is particularly sparse. Previously reported cases during pregnancy were managed with local triamcinolone injection, drainage followed by postpartum excision, or medical inflammation control followed by surgery, but these isolated experiences cannot establish a standard protocol. A retrospective study of rotational gland dissection in 129 patients with refractory granulomatous mastitis reported a recurrence rate of 3.10% at a median follow-up of 56 months, but that cohort was not limited to accessory-breast GLM and therefore does not establish the outcome of the procedure in this rare anatomical presentation.

For this patient, the authors selected complete excision because the mass had irregular, poorly defined borders, and simple removal of the palpable portion was considered insufficient. The operation addressed inflamed tissue, abscesses, dilated ducts and affected skin, with a local flap used to restore the axillary contour. Because GLM is inflammatory rather than malignant, the authors stated that the extent of surgery should be tailored to the lesion rather than governed by an absolute requirement for histologically negative margins. Drain output was 10 mL on each of the first two postoperative days, reached zero on day three, and the drain was removed on day four. Sutures were removed on day 14 before discharge, and the bilateral axillary incisions had healed well. Ultrasound one year after surgery showed no abnormalities. This single outcome demonstrates that excision with reconstruction was feasible in the reported case, but it does not prove superiority over medical treatment or establish recurrence risk. The authors concluded that management should be individualized according to disease severity, lesion extent, patient characteristics and preferences, and that additional studies are needed to develop diagnostic criteria and standardized treatment recommendations for this rare presentation.

Subject of Research: Clinical presentation, diagnosis and management of granulomatous lobular mastitis in accessory breast tissue

Article Title: Granulomatous lobular mastitis involving accessory breast tissue: a case report and review of the literature

Article References: Li, X.-F., Meng, S.-S., Wang, T.-S., Zuo, X.-M., Gao, X., & Shi, X.-G. (2026). Granulomatous lobular mastitis involving accessory breast tissue: a case report and review of the literature. Frontiers in Oncology, 16, Article 1960013. https://doi.org/10.3389/fonc.2026.1960013

Image Credits: AI Generated

DOI: 10.3389/fonc.2026.1960013

Keywords: granulomatous lobular mastitis, accessory breast tissue, axillary inflammation, breast histopathology, breast ultrasound, case report, narrative review, surgical excision, flap reconstruction, rare disease, Granulomatous, lobular