An indirect consequence of the improved long-term survival seen in patients with breast cancer (BC) is the increased risk of hematologic malignant neoplasms (HM). This study aimed to analyze the role of postoperative treatment for BC in the development of subsequent HM. Using the French National Health Data System, we examined the HM risks in patients diagnosed with an incident primary breast cancer between 2007 and 2015, who underwent surgery as first-line treatment for BC. Main outcomes were acute myeloid leukemia (AML), Myelodysplastic syndrome (MDS), myeloproliferative neoplasms (MPNs), multiple myeloma (MM), Hodgkin’s lymphoma or non-Hodgkin’s lymphoma (HL/NHL), and acute lymphoblastic leukemia or lymphocytic lymphoma (ALL/LL). Analyses were censored at HM occurrence, death, loss to follow up, or December 2017. The risk of each type of HM was compared according to the initial postoperative treatment of breast cancer. Of a total of 324,056 BC survivors, 15.5% underwent surgery only, 46.7% received radiotherapy after surgery, 4.3% received chemotherapy after surgery, and 33.5% received all three modalities. Overall, 2236 cases of hematologic malignancies occurred. Compared to the surgery alone group, AML was significantly increased after surgery plus radiation (aHR, 1.5; 95% CI, 1.0–2.1), surgery plus chemotherapy (aHR, 2.1; 95% CI, 1.2–3.6) and all modalities (aHR, 3.3; 95% CI, 2.3–4.7). MDS was significantly increased after surgery plus chemotherapy (aHR, 1.7; 95% CI, 1.1–2.5) or after all modalities (aHR, 1.4; 95% CI, 1.1–1.8). HL/NHL were significantly increased only in the radiotherapy and surgery group (aHR, 1.3; 95% CI, 1.0–1.6). A nonsignificant increase of ALL/LL (aHR, 1.8; 95% CI, 0.6–3.5) was noted after chemotherapy and with all three modalities (aHR, 1.4; 95% CI, 0.7–2.8). Our population based study revealed increased risks of various HM associated with postoperative BC treatment. The added benefit of chemotherapy and radiation therapy should take into consideration these long-term complications.