Background: Denovo metastatic young breast cancer (dnmYBC), defined as age <40 years, is a challenging entity, with a significant burden and sparse data from low and middle-income countries.

Method: We analysed the prospectively collected data of dnmYBC women from 2015 to 2016.

Results: There were 188 dnmYBC with a median age of 35.5 years. Of these, hormone receptor positive (HR+) were 72 (38.3) %, triple-negatives (TNBC) were 45 (23.9) %, Human Epidermal Growth Factor Positive (HER2+) were 42 (22.4) % and triple positives were 29 (15.4) %. TNBC women predominantly had visceral 40 (88.9%) metastasis, HR+ had nodal 51 (70.8%) and skeletal 10 (13.8%), while HER2+ women had higher brain metastasis (BM) 16 (38.1%).

At a median follow-up of 39.8 [Interquartile range (IQR): 24–55.5] months, the median event-free survival (EFS) was 9.3 (95% CI; 8.1–10.4) months for the entire cohort and 1-year, 2-year and 3-year predicted EFS were 47.8%, 13.4% and 3%, respectively. The median EFS was superior in HR+ women.

[15.7 months, hormone receptor (HR)−0.53;95% CI-9.8–21.7; p-0.013] versus (11.4 months, 95 %CI-5.9–16.8) in TNBC versus (7.7 months, 95% CI-6.0–9.5) in HER-2 + women and without BM at baseline [9.3 versus 3.0 months (with BM), HR-5.65; CI-1.72–17.9; p-0.001]. Median EFS was superior in the treatment-naïve (155, 82.4%) versus prior-treated (33, 17.5%) women, 35.5 (95% CI:12.24–58.72) versus 12.4 (95% CI:11.45–13.51) months; p-0.000]. The HER2+ women who received targeted therapy in the first line had a significantly superior median EFS of 13.0 versus 7.7 months (HR -0.465:CI 0.22–0.57: p-0.038).

Conclusion: Denovo mYBC is associated with an aggressive course, poor prognosticators include HR negative disease, brain metastasis, inadvertent prior treatment and inadequate access to targeted therapies. Early diagnosis, prompt treatment and expanding accessibility are warranted to improve care.