Andre Mattar, MD, PhD, and colleagues presented at the 2022 San Antonio Breast Cancer Symposium to discuss their study, “Clinical and pathological differences between HER2-low and other cancer subtypes in breast cancer patients,” which assessed the frequency and clinicopathological differences between cancer subtypes and survival rates.

The study included patients with breast cancer who were diagnosed between 1987 and 2021 in the Pérola Byington Hospital database. Exclusion criteria were bilateral disease, if the patient had participated in clinical studies, or if there was incomplete data.

The primary endpoint was overall survival stratified by cancer subtype. Secondary endpoints included clinicopathological differences between cancer subtypes and probability of death.

The study authors used t-test and the chi-square test to analyze the associations between the subgroups; multivariate analysis was used for odds ratios (OR) and 95% confidence intervals (CI) for the death outcomes. Survival analysis used Cox regression with the Log-rank method.

 A total of 11,234 patients were included in this study, consisting of 4,541 (40.42%) with the luminal cancer subtype; 2,955 (26.30%) with HER2-low; 2,242 (19.96%) with triple negative; and 1,496 (13.32%) with HER2 overexpression.

Statistically significant differences between the subtypes were presented in the following areas: age, self-reported ethnicity, body mass index, presence of comorbidities, clinical stage, nuclear grade, histological grade, family history, radiotherapy, chemotherapy, surgery, local, and systemic recurrence, and death.

There was a 44.8% greater probability of death in patients with HER2 overexpression vs HER2-low (OR 1.448, 95% CI 1.046-2.004, P = .026), and patients with triple-negative cancer had a 26.1% lower probability vs HER2-low (OR 0.739, 95% CI 0.562-0.969, P = .0229). There was no statistically significant difference between the luminal subtype vs HER2-low.

Overall survival had a statistically significant difference between subtypes when compared to 12 years for HER2-low: Luminal and HER2 overexpression showed a median of 12 years and 15 years, respectively, while no statistical difference was shown for triple-negative BC.

“This study in breast cancer patients demonstrates significant differences between cancer subtypes, with a higher probability of progression to death for patients with HER2 overexpression, while patients with luminal subtype had a lower probability, when compared with HER2-low,” the authors concluded, adding that more studies are needed to clarify the impact of these differences on response to therapy.

Mattar A, Amorim A, Diogenes M, et al. Clinical and pathological differences between HER2-low and other cancer subtypes in breast cancer patients. Presented at: 2022 San Antonio Breast Cancer Symposium. December 6-10, 2022. Poster P1-04-17.