Abstract
BACKGROUND: Among human epidermal growth factor receptor 2 (HER2)-positive breast cancer patients who receive anti-HER2 treatment, a noteworthy correlation between pathological complete response (pCR) and longer survival has been observed. The rate of pCR varies with the tumor's degree of HER2 protein expression. The aim of this study was to assess the correlations between clinicopathological characteristics, magnetic resonance imaging (MRI) parameters, and pCR in breast cancer with different HER2 subcategories. METHODS: A total of 281 invasive breast cancer patients diagnosed with HER2-positivity were included. HER2-positive translated to immunohistochemistry (IHC) 3+ or IHC 2+/fluorescence in situ hybridization (FISH)(+). All enrolled patients underwent baseline MRI examination and received neoadjuvant chemotherapy, dual anti-HER2 therapy, and subsequent therapeutic surgery from January 2021 to May 2022. A logistic regression model was used to evaluate the effects of covariates on pCR. RESULTS: Compared to the IHC 2+/FISH(+) group, patients with IHC 3+ tumors had a higher pCR rate (58.1% vs. 26.7%, P<0.001), clinical stage (58.6% vs. 40%, P=0.038), apparent diffusion coefficient (ADC) value (0.96 vs. 0.88 mm(2)/s, P=0.004), and were more likely to be estrogen receptor (ER) negative (55.9% vs. 31.1%, P=0.002) and progesterone receptor (PR) negative (72.5% vs. 46.7%, P=0.001). In both groups, univariate analysis showed that the pCR group more often had ER-negative and PR-negative status than the non-pCR group (P<0.001). The final multivariable analysis showed that ER-negativity was associated with pCR in the IHC 2+/FISH(+) group (P=0.004). ER-negativity and the longest diameter were two independent predictors of pCR in the IHC 3+ group (P<0.001 for ER, P=0.026 for longest diameter). CONCLUSIONS: The IHC 3+ group had a higher pCR rate than the IHC 2+/FISH(+) group. Along with clinicopathological characteristics, MRI parameters were supplemental predictors of pCR, particularly in IHC 3+ patients.