Background: Adjuvant systemic therapy in women with early ER+/HER2+ BC usually includes ChT, trastuzumab (T) and endocrine therapy (ET). High level of TILs is associated with better outcome in HER2+ disease. Here we explore the outcome and prognostic role of TILs in women with early ER+/HER2+ BC in whom ChT was omitted. Methods: Women with ER+ (IHC ≥ 1%) and HER2+ (IHC3+ and/or FISH ratio ≥ 2.0) early BC who underwent surgery between years 2006 and 2016 at the Institute of Oncology Ljubljana and did not receive adjuvant ChT were eligible for this study. Hematoxilin and eosin slides of primary tumors were retrieved and evaluated for the percentage of stromal TILs. Distant disease-free survival (DDFS) was estimated by the Kaplan-Meier method. The association between DDFS and TILs level was explored in the Cox proportional hazard model. Relative survival was used for estimating the probability of dying due to the breast cancer or other causes. Results: During the 10-year period 86 (29.4%) out of 292 women with early ER+/HER2+ BC who underwent surgery did not receive adjuvant ChT. ChT was omitted due to the stage I disease (n=30), comorbidities (n=25), older age (n=19), refusal of treatment (n=9) and other causes (n=3). Five (5.8%) and 81 (94.1%) women received T and ET, respectively. Their median age was 65.8 yrs (IQR 55.7, 75.6 yrs) and 45 (52.3%) had stage I disease. There were 53 (61.6%), 24 (27.9%) and 9 (10.4%) women with low (<10%), intermediate (≤10% to <40%) and high (≥ 40%) level of TILs, respectively. After median follow-up of 10 years 28 events (distant recurrence or death) occurred. The 10-year DDFS for those who did not receive ChT due to the stage I disease, comorbidities and older age was 91% (95% CI, 0.79 to 1.00), 38% (95% CI, 0.18 to 0.75]) and 26% (95% CI, 0.10 to 0.66) (p˂0.0001), respectively. After excluding women with stage I disease the estimated probability of dying due to the breast cancer and due to other causes was 26.7% and 26.5%, respectively. Overall, for every 10% increase in TILs the risk of distant recurrence or death was reduced for 18% (HR=0.82; 95% CI, 0.64 to 1.05) (p=0.11). In the multivariable Cox model, higher TILs level was a significant predictor of better DDFS (HR 0.75; 95% CI, 0.57 to 0.98) (p=0.041) (Table). Conclusions: Women with stage I ER+/HER2+ BC who do not receive adjuvant ChT and T but do receive adjuvant ET may still have a very good outcome. In contrast, survival of women who do not receive adjuvant ChT and T for other reasons is poor; however, only a half of those deaths are related to BC. TIL is a favourable prognostic biomarker which might be helpful when de-escalation of systemic therapy in women with ER+/HER2+ BC is considered.