Abstract P1-08-25: The differential diagnosis of a large breast mass in a young woman

Abstract A healthy 28-year-old G5P3A2, nonpregnant woman presented to the emergency room for evaluation of a 7 cm right breast mass. She recently immigrated to the United States from eastern Europe and had no established primary care provider. Patient reported a breast mass increasing in size over two months and an unintentional weight loss of 5 kg. She visited an urgent care center one month before presentation and was prescribed amoxicillin-clavulanate, but her symptoms had not resolved. The patient was not on hormonal contraception and her menses occurred on a regular, monthly basis. She had no known family history of cancer. At her visit, the patient was afebrile, heart rate was 92, and blood pressure was 115/67. Examination revealed a 7 x 8 cm right breast mass at 7 o’clock with tenderness to palpation, and right axillary fullness and discomfort to palpation. No skin changes were identified. There was no cervical or supraclavicular adenopathy. Breast ultrasound showed diffuse masslike region in the right breast from 6 – 9 o’clock, predominantly tubular in nature, with associated abnormal segmental ducts. A mammogram revealed a right inferior breast mass with associated periareolar skin thickening, in the background of heterogeneously dense breasts. Left breast was radiographically unremarkable. Ultrasound-guided breast biopsy was performed, initially yielding mobile debris, 5 cc of purulent fluid, and 5 cc of bloody fluid. After the initial aspiration, a core biopsy of the underlying persistent mass was taken. Baseline laboratory studies with complete blood count and basal metabolic panel were notable only for WBC at 11.5x109 cells/L. CT chest, abdomen, and pelvis with contrast showed no evidence of metastatic disease. Differential diagnosis of a breast mass in a young woman includes benign proliferative changes, malignancy, hematoma, papilloma, cyst, galactocele, mastitis, fat necrosis, or infection. Pathology from the right breast biopsy revealed benign breast tissue with acute inflammation, granulation tissue, microabscess formation, and histiocyte aggregates. Gram stain, fungal studies (PAS), and AFB for mycobacterial organisms were negative. A bacterial PCR 16s rDNA was sent on paraffin-embedded tissue to a reference lab and not detected. Ultimately, aerobic culture from broth only (which generally indicates a low bacterial burden or possible contamination), yielded Corynebacterium species. Final pathologic diagnosis was cystic neutrophilic granulomatous mastitis (CNGM), a rare breast inflammatory process usually due to Corynebacterium species infection. CNGM occurs in reproductive-aged women with a history of pregnancy and often mimics breast carcinoma. Radiology noted pathologic concordance with imaging. The patient was treated with trimethoprim/sulfamethoxazole for 10 days and referred to a breast surgeon. However, her symptoms did not improve, and a repeat ultrasound 14 days later showed increased size of the abscess measuring 4 x 1.5 x 4.3 cm. Repeat ultrasound-guided aspiration was performed and the patient was prescribed doxycycline for one month. Though she experienced increased pain midway through treatment, she ultimately had improvement in her symptoms at her follow-up visit 74 days from presentation. Follow-up breast ultrasound performed the same day did not demonstrate evidence of fluid collection or abscess, but again noted an unchanged irregular mass associated with small loculated areas of fluid. This case brings to light the medical and surgical differential diagnosis beyond malignancy for a large breast mass in a young, nonpregnant woman presenting to an oncology clinic. A table with differential diagnosis, images and references will be provided for the poster if accepted. Citation Format: Hetal Mistry, MacKenzie Adams, Li Juan Wang, Charu Taneja, Stephanie Graff, Mary Anne Fenton. The differential diagnosis of a large breast mass in a young woman [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P1-08-25.