Adjuvant trastuzumab has been associated with superior survival in women with ≥ T1c or node-positive HER2-positive early-stage breast cancer; however, there is a lack of phase III trials in women with T1a/bN0 disease. Our study aimed to assess the outcomes of women with HER2-positive T1a/bN0 breast cancer who received adjuvant trastuzumab in Saskatchewan, Canada. We evaluated all women diagnosed with HER2-positive T1a/bN0 breast cancer in Saskatchewan between 2008 and 2017. We performed Cox proportional multivariable analysis to determine factors correlated with survival. In addition, inverse probability treatment weighting (IPTW) using propensity score was performed to assess benefit of adjuvant trastuzumab. Ninety-one eligible women with a median age of 61 years (range 30–89) were identified. Thirty-nine (43%) women received adjuvant trastuzumab. Women who received trastuzumab were younger and had a higher rate of T1b disease. Overall, 3% of women who received trastuzumab compared to 12% of women who did not receive trastuzumab developed breast cancer recurrence (p = 0.23). Five-year disease-free survival (DFS) of women who received adjuvant trastuzumab was 94.8% compared to 82.7% of women who did not receive trastuzumab (p = 0.22). Five-year overall survival was 100% of women who received trastuzumab compared to 90.4% of women who did not receive adjuvant trastuzumab (p = 0.038). In the multivariable analysis, grade III tumors were correlated with inferior DFS (hazard ratio [HR] 5.5, 95% CI [1.7–17.7]). The propensity score using the inverse probability of treatment weighting showed that lack of adjuvant trastuzumab was correlated inferior DFS, with an HR of 4 (95% CI 1.05–15.5). Women with HER2-positive T1a/bN0 breast cancer had overall low recurrence of breast cancer. However, the results of this exploratory analysis indicate that women who received adjuvant trastuzumab had better survival.

Background: Oncotype DX (ODX) assay identifies specific subset of patients with hormone-receptor (HR)-positive breast cancer (BC) who would benefit the most from adjuvant chemotherapy (CT). This study aimed to examine inter-agreement among several medical oncologists, as well as each oncologist intra-agreement on adjuvant CT decisions before and after Oncotype DX.Methods: The data of 145 patients with HR-positive, HER2 negative BC were reviewed in retrospect. Traditional histopathological information with and without ODX RS was sent to 16 oncologists. The inter and intra-observer agreement among oncologists on prescribing adjuvant CT before and after ODX RS result were assessed. The result of ODX RS was interpreted as continuous variable and as per-risk level; low (0-17), intermediate (18-30) and high risk (! 31) groups. A P-value of < 0.05 was considered significant. Results:The mean age at diagnosis AE SD was 51.9 AE 9.4 years. 76 patients (52.4%) were postmenopausal. The mean ODX RS was 17.8 AE 8.6 where 54.5% was low, 37.9% was intermediate and only 7.6% was high, respectively. Grade 2 (53.1%) and T(1) (49%) BC accounted for the majority. Positive (1-3) lymph nodes reported in onethird. The agreement among oncologists improved with the addition of ODX result from fair to moderate (kappa ¼ 0.52; p <0.001). The addition of ODx RS result avoided CT in 20.4% and identified 9.1% as candidates for adjuvant CT (Kappa ¼ 0.38; p <0.001). On average, an oncologist's decision of prescribing adjuvant CT pre and post ODx had an agreement in 70.6% of the cases. The table shows agreement and disagreement between pre & post-ODX decision. Conclusions:We conclude that Oncotype DX RS boosted the level of agreement among oncologists and led to a decrease in the use of adjuvant chemotherapy compared to the pre-Oncotype DX recommendations.Legal entity responsible for the study: The authors.