Abstract P1-07-10: Immunohistochemical (IHC) marker discordance between primary breast cancer biopsy and recurrent cancer: Would IHC testing of the surgical breast or lymph node have altered treatment?

Objective: Based on emerging data on tumor heterogeneity and the evolutionary branching of tumor cells, tumor cells in the lymph node may represent more virulent clones with the inherent capability of metastasis. IHC discordance from original cancer diagnosis to recurrence is documented to occur in up to 20% of cases, raising the question if characterization of these likely more virulent cells would more accurately guide treatment and predict prognosis. Our pilot study sought to determine if crucial clinical information is gained by IHC testing of the surgical breast or lymph node specimens at the time of initial surgery. Methods: Using the cancer registry and oncology records, all invasive breast cancers diagnosed after 2001 with subsequent recurrence were identified. Cases missing all IHC data were disqualified. We then evaluated ER and HER2 of the primary cancer biopsy and recurrence biopsy to identify discordances. Those with discordances who had surgical breast and lymph node specimens available were accessed, tested, and evaluated by our breast cancer pathologist. Results: A total of 128 recurrence cases with partial or complete primary and recurrence IHC data were identified. Of the 95 initially ER positive cases with recurrence IHC available, 13/95 had discordant, or ER negative, recurrence. Additionally, 5/27 initially ER negative tumors, 3/14 initially HER2 positive tumors, and 6/69 initially HER2 negative tumors had discordant recurrence results. In 128 cases, 27 cases were identified to have ER or HER2 discordance from primary biopsy diagnosis to recurrence. Of all cases with original surgical breast or positive lymph node specimen available, 9 markers on 7 patients were performed for our pilot study. One of seven surgical breast specimens and one of two lymph node specimens were concordant with the recurrence, but not the initial biopsy. The tested surgical breast was ER positive, while the surgical lymph node was HER2 positive, concordant to their recurrences, but discordant with initial biopsy. Conclusion: Tumor discordance of the original cancer biopsy and recurrence is not uncommon. Our pilot study demonstrated that ER and HER2 discordance occurred in 15% and 11% of cases, respectively. Though our pilot study was limited by small sample size, we found that IHC testing of the surgical breast and lymph node specimen may provide additional clinical information and affect management. Of the two cases that had a positive lymph node available, one was HER2 positive and concordant with the recurrence. Of the seven breast specimens tested, one was ER positive and concordant with the recurrence. Had IHC testing been performed at that time of surgery, adjuvant treatment management would have been altered. Further testing of our IHC discordant recurrence patient population will be pursued to investigate the potential benefits of surgical breast and lymph node IHC testing. Citation Format: Michele M Gage, Martin Rosman, Charles Mylander, Crystal Tran, Rubie S Jackson, Lorraine Tafra. Immunohistochemical (IHC) marker discordance between primary breast cancer biopsy and recurrent cancer: Would IHC testing of the surgical breast or lymph node have altered treatment? [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P1-07-10.