Receptor expression testing of the synchronous axillary nodal metastasis in early-stage breast cancer: Comparison of primary tumor and its draining nodes.

Abstract

e12542 Background: Early stage (Stage I-III) human epidermal receptor -2 (HER2) positive and triple negative breast cancers (TNBC) tend to behave more aggressively than hormone positive breast cancers with higher and earlier incidences of recurrences. Oftentimes, testing for receptor subtypes is done only on the primary tumor and not on the synchronous axillary metastasis, with the assumption that the axillary metastasis is congruous to the primary lesion. Current guidelines also do not specify a requisite to do this testing. Information about the receptor expression types is fundamental for the treatment of breast cancer. We aimed to determine if there is significant discordance between the primary and ipsilateral axillary metastasis in early-stage breast cancer. Methods: We conducted a retrospective analysis via electronic medical record review of a large institutional database from 2008 to 2020. Sample for this study included all patients with a diagnosis of early-stage breast cancer (Stage I - III) with triple negative or HER2 positive tumors. Data on demographics, comorbidities, receptor status, staging, and mortality were collected. Results: Electronic charts from 448 patients were reviewed. 140 patients had axillary node positive disease. 40 (29%) of the 140 patients underwent testing for receptors subtypes on both primary and axillary nodal metastasis. 8 (20%) of the 40 patients had discordance in their receptor subtype expressed in their respective axillary nodal metastasis. 32 (80%) of the 40 patients had axillary receptor expression congruous to the primary tumor. At the time of our review, there was no statistically significant mortality between discordant compared to concordant group (13% vs 20%; p=0.54). 2 patients were lost to follow up. Conclusions: Our data suggests that one in every five axillary metastatic breast cancers can have receptor subtypes discordant compared to the receptors expressed on the primary tumor. Knowledge about any such discordance between the primary and respective axillary metastasis has a consequential impact on the treatment approach for early-stage breast cancer. This is especially true if the patient’s nodal metastatic lesions indeed prove HER2 receptor positivity or do not express any receptors (TNBC). Consequently, patients may be being deprived of benefits from advances in treatment of these cancers, such as targeted therapies towards HER2 receptor, hormonal treatments when indicated, or the utilization of neoadjuvant chemotherapy. A strong case can be thus made to revise current standards to include receptor testing on all primary and synchronous axillary metastasis. Further testing is needed to validate our findings.