We assessed long-term associations of Granulocyte-Colony Stimulating Factors (G-CSF) use with patient-reported outcomes (PROs) and hematologic toxicity among chemotherapy-treated, early-stage breast cancer patients in CANTO (NCT01993498). Among 2920 patients longitudinally followed-up until year-4 after diagnosis, 49% used G-CSF. In multivariable-adjusted mixed-models, EORTC QLQ-C30 pain and summary score were not substantially different between groups (overall adjusted mean difference, use vs no-use 95%CI: +1.27 -0.33 to +2.87 and −1.01 -1.98 to −0.04, respectively). PROs were slightly worse at year-4 among patients receiving G-CSF, although differences were of trivial clinical significance. No major differences were observed in leukocyte or platelet count over time. •Studies on long-term side effects of G-CSF, including on quality of life, are lacking.•We evaluated PROs and hematological values until year-4 after diagnosis among women with early breast cancer receiving G-CSF.•49% women treated with adjuvant chemotherapy in CANTO (N = 2920) used G-CSF.•Long-term PROs and hematological values were not substantially different in women using G-CSF or not.•There were slightly worse outcomes at year-4 in patients using G-CSF, although of trivial clinical significance.