A team of researchers led by Charles E. Geyer, MD, compared breast cancer-specific mortality (BCSM) in patients with invasive lobular breast cancer (ILC) and invasive ductal carcinoma (IDC). They aimed to evaluate the performance of the 21-gene Breast Recurrence Score (RS) commercial assay in ILC by linking its prognostic results to individuals in the Surveillance, Epidemiology, and End Results (SEER) registry.
In the study, investigators concluded that RS results successfully predicted BCSM in patients with ILC-subtype hormone receptor-positive and HER2-negative breast cancer, regardless of node-positive or node-negative disease status. Findings were featured as a poster at the ASCO 2023 Annual Meeting in Chicago, IL.
The authors noted that this report was an update to a 2017 study on the performance of RS for 5-year BCSM prognosis using SEER data linked in 2015. The follow-up analysis compared RS results and 9-year BCSM outcomes from a linked-data update in 2019.
Assay Prognosis is Accurate in ILC Breast Cancer
Eligible individuals had 0-3 positive axillary nodes at initial surgery, no prior malignancies, and available RS results. Patients were classified as ILC or IDC using International Classification of Diseases for Oncology 3 (ICD-O-3) codes, and multivariable Cox models were used to compare RS and BCSM outcomes.
Of 89,818 patients screened, 9835 (11.0%) had ILC and 64,669 (72.0%) had IDC. In the ILC group, 12.5% of patients were N1 status, 28.4% were grade 1, 63.7% were grade 2, and 7.9% were grade 3. The median follow-up was 94 months and the median age was 60 years.
Specific rates of chemotherapy use and 9-year BCSM according to RS results in patients with node-negative ILC include;
| RS Result | Number of Patients | Chemotherapy Use | 9-Year BCSM |
| 0-15 | 3899 | 6.5% | 2.6% (95% CI, 2.0-3.3) |
| 16-20 | 2517 | 17.0% | 2.6% (95% CI, 1.9-3.6) |
| 21-25 | 1471 | 34.0% | 4.8% (95% CI, 3.6-6.5) |
| 26-100 | 724 | 57.2% | 8.2% (95% CI, 6.1-11.0) |
Rates in patients with node-positive ILC include;
| RS Result | Number of Patients | Chemotherapy Use | 9-Year BCSM |
| 0-15 | 613 | 22.7% | 4.9% (95% CI, 2.6-9.4) |
| 16-20 | 347 | 37.8% | 8.1% (95% CI, 5.2-12.5) |
| 21-25 | 170 | 44.1% | 9.8% (95% CI, 5.6-16.8) |
| 26-100 | 94 | 63.8% | 16.2% (95% CI, 9.9-25.8) |
The authors noted that both chemotherapy use and BCSM increased with RS results in both groups. In addition, the association between RS results and BCSM was maintained after adjusting for age, race, tumor grade, tumor size, nodal status, and histologic subtype (P<.001).
Dr. Geyer and colleagues concluded that results from RS successfully predicted BCSM at 9 years in patients with hormone receptor-positive and HER2-negative breast cancer, including those with the less-common ILC subtype.
More highlights from the ASCO 2023 Annual Meeting
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