Main outcomes were acute myeloid leukemia (AML), Myelodysplastic syndrome (MDS), myeloproliferative neoplasms (MPNs), multiple myeloma (MM), Hodgkin lymphoma or non–Hodgkin lymphoma (HL/NHL), and acute lymphoblastic leukemia or lymphocytic lymphoma (ALL/LL).

Among a total of 122 373 BC survivors, 38.9% received chemotherapy only, and 61.1% received chemotherapy + G‐CSF. Overall, 781 cases of hematologic malignancies occurred.

We observed a non‐significant increase in the risk of AML (aHR, 1.3; 95% CI, 1.0‐1.7), of MDS (aHR, 1.3; 95% CI, 0.9‐1.8), and of ALL/LL (aHR, 2.0; 95% CI, 1.0‐4.4) among patients treated by chemotherapy + G‐CSF compared to chemotherapy only.

In analyses by dose, we observed a slight increase in the risk of AML (1‐3 doses: aHR, 1.2; 95% CI, 0.8‐1.7 / 4+ doses: aHR, 1.3; 95%CI, 1.0‐1.8) and of MDS (1‐3 doses: aHR, 1.1; 95% CI, 0.7‐1.7 / 4+ doses: aHR, 1.4; 95%CI, 1.0‐1.9), a significant increase in risk of ALL (1‐3 doses: aHR, 1.5; 95% CI, 0.5‐3.9 / 4+ doses: aHR, 2.3; 95%CI, 1.0‐5.1) with increasing cycles of G‐CSF.

Our population based study showed that the ALL/LL was the only HM at increased risk with the use of growth factors with a possible dose effect relationship.

Our data regarding the risk of all the other HM are reassuring.