Clinicopathologic Features and Pathogens of Granulomatous Lobular Mastitis.

Background: Granulomatous lobular mastitis (GLM) is a rare, benign, and complex breast disease that can be easily misdiagnosed as breast cancer. The etiology of GLM is unclear, and optimal treatment has not been established. Methods: Medical records for 333 patients with GLM in recent 5 years at Longhua Hospital, Shanghai, China, were analyzed. Potential pathogens in 33 fresh tissue specimens were also analyzed using 16S rDNA sequencing technology, matrix-assisted laser desorption ionization time of flight mass spectrometry, and bacterial cultures. Results: The median age of patients was 32 years (range 22-47 years). Among 333 patients, 38.7% displayed elevated prolactin, while 23.7% displayed high interleukin-2. In the granulomatous lesion, CD3-positive T lymphocytes were significantly more than CD20-positive B lymphocytes around the vacuoles or microabscesses. Gram-positive organisms were observed in 82 cases, including in 22 cases from fresh tissue specimens. Thirty-three cases yielded associated pathogens and all displayed multiple pathogenic infections, as identified using 16S rDNA sequencing technology. Pathogenic infections were further identified as belonging to 16 main genera and 8 main pathogenic species. Conclusions: GLM displays distinct histological and clinical features similar to those that have been previously reported in the literature. Using 16S rDNA sequencing technology, all of our cases demonstrated multiple pathogenic infections, which provided more useful information for clinical treatment.