SAT612 Granulomatous Mastitis: An Unusual Presentation Of Prolactinoma

Disclosure: H.R. Alkaissi: None. E. Kim: None. S. McFarlane: None. Background: Granulomatous mastitis (GM) is a rare, benign inflammatory breast disease of unclear etiology with clinical presentation that is similar to inflammatory breast cancer and periductal lobular mastitis. It occurs mainly in younger females and during the postpartum period. Prolactin (PRL) is an essential hormone of pituitary and extrapituitary origin that promotes lactation and the development of mammary glands within breast tissues. In addition to its lactogenic effect, it has over 300 other effects, several of which are immunomodulatory, including the expression and secretion of proinflammatory cytokines from macrophages. Clinical Case: A 37-year-old African American woman presented with right breast pain and swelling for a few weeks. Her medical history includes amenorrhea for five years. She is gravida 1, para 1 with normal spontaneous vaginal delivery at the age of 20. Physical exam showed non-bloody, non-purulent nipple discharge bilaterally, otherwise unremarkable. A breast ultrasound showed a 1 cm complex cystic mass. Biopsy showed benign breast tissue, with noncaseating granulomas formed by macrophages (CD68 positive on immunohistochemistry). Ziehl-Neelsen staining for acid-fast bacilli was negative. Staining for fungi was also negative. Prolactin level was 237 ng/mL. TSH, IGF-1, and ACTH were within normal. Pituitary MRI showed a focus of abnormal signal and diminished enhancement measuring 2.8x3.2x4.2 mm within the left side of the pituitary gland is compatible with a microadenoma. The patient was started on bromocriptine 2.5mg daily. Discussion: Our patient represents a rare case of granulomatous mastitis in the setting of microprolactinoma, likely long-standing, given the five years history of amenorrhea. The immunomodulatory effect of PRL on several immune system cells, including B-cells, T-cells, and macrophages, might be an underlying mechanism. In a recent study of 25 samples of GM, metagenomics studies identified unusual organisms in 68% of the samples. Of these, Corynebacterium kroppenstedtii was the most common (60%), followed by Pseudomonas oleovorans (16%), Epstein-Barr virus (4%), Acinetobacter baumannii (4%), and Tepidiphilus thermophilus (4%). In addition, 50% of the patients had elevated PRL, and elevated immunological markers, such as C3 and IgA [1]. This suggests that GM results from an interaction between the presence of certain pathogens in a host with elevated PRL that mediates proinflammatory response. References: 1. Bi J, Li Z, Lin X, et al. Etiology of granulomatous lobular mastitis based on metagenomic next-generation sequencing. Int J Infect Dis. 2021 Dec;113:243-250. doi: 10.1016/j.ijid.2021.10.019. Epub 2021 Oct 19. PMID: 34673215. Presentation: Saturday, June 17, 2023