Clinicopathological Features of Mammary Adenoid Cystic Carcinoma
A retrospective study found a positive correlation between MYB gene abnormalities and HER2 status among patients with mammary adenoid cystic carcinoma (AdCC). It was also noted that mammary AdCC should be considered a distinct triple-negative breast cancer (TNBC) rather than low-grade TNBC.
The study authors described AdCC as “characterized by the presence of the distinctive MYB-NFIB fusion,” but add that “pathologists currently have an incomplete understanding” of mammary AdCC subtypes.
This retrospective study included data from 25 patients with mammary AdCC who were treated between January 2013 to November 2024. All specimens from the patients underwent histomorphological examination, immunohistochemical (IHC), and fluorescence in situ (FISH) testing. Of the 25 overall patients, 21 were classified as classic AdCC (C-AdCC), 2 as solid-basaloid AdCC (SB-AdCC), and 2 as AdCC with high-grade transformation. In terms of treatment, 5 patients underwent modified radical mastectomy, 15 underwent simple mastectomy with sentinel lymph node biopsy, 4 underwent breast-preserving surgery with sentinel lymph node dissection. There was 1 patient who received neoadjuvant chemotherapy (3 cycles of doxorubicin liposomal and cyclophosphamide) followed by simple mastectomy with sentinel lymph node dissection. There were 2 cases with axillary lymph node metastasis and 23 with no lymph node metastasis. Follow-up duration ranged from 6 to 136 months, with 3 cases lost to follow-up. There was 1 patient who died at 60 months while 21 patients remained in good general condition without recurrence or metastasis.
Of the total 25 specimens, 21 were ER-negative and 4 were ER-positive with a positivity index of 2% to 20%; all the specimens were PR-negative; and 24 specimens were AR-negative and 1 was “weakly AR-positive” with a positivity index of 5%. By IHC testing, there were 14 cases of HER2-negative (HER2 IHC 0) and 11 cases of HER2-low. In the 11 HER2-low cases, 9 were HER2 IHC 1+ and 2 were HER2 IHC 2+. The cases of HER2 IHC 2+ were confirmed to be negative for amplification via FISH testing.
Among the HER2-negative specimens, there were 5 with MYB gene abnormalities (MYB break-apart, n = 4; MYB/NFIB fusion, n = 1). Among the HER2-low specimens, there were 9 with MYB gene abnormalities (MYB break-apart, n = 8; MYB/NFIB fusion, n = 1). With Fisher’s exact test, there was a statistically significant positive correlation between HER2-low expression and MYB gene abnormalities (P = .042). There was also no statistically significant association between HER2 status and other clinicopathological parameters, such as age, tumor size, Ki-67 index, lymph node metastasis, and pN stage (P > .05).
The study authors noted the importance of understanding “histological morphology, IHC profiles, and molecular alterations across its pathological subtypes” to provide both an accurate diagnosis and “individualized precision treatment strategies.” They concluded that the correlation between HER2-low expression and MYB gene abnormalities observed in this study “provides a critical foundation for developing combined targeted therapies and prognostic stratification in affected patients.”
Source:
Xu X, Yu S, Qu W, Chen Y, and Yang L. Analysis of clinicopathological features and clinical significant in 25 cases of mammary adenoid cystic carcinoma. BMC Women’s Health. Published online October 6, 2025.
