A recent study in Blood analyzed the incidence of venous thromboembolism (VTE) in relation to the time window of breast cancer treatment, revealing its dramatic variation in the course of breast cancer treatment. The current study of more than 13?000 women diagnosed with breast cancer between 1997 and 2006 was followed for VTE incidence from the date of diagnosis by a validated algorithm combining the 10 criteria of the International Classification of Diseases CVTE, anticoagulation norms and mortality data. vte occurred in 611 (4.6%) women during the follow-up period, i.e. 0.84%/year, although this may underestimate the actual incidence of VTE (including asymptomatic VTE that can only be detected by a series of tests). Multivariate correction analysis suggested that the baseline risk factors of advanced age, overweight/obesity, and distant metastatic disease significantly increased the incidence of VTE. The accompanying data illustrate how the incidence of VTE changes over time when patients receive chemotherapy and endocrine therapy or surgery. Compared with patients who did not undergo surgery, the incidence of VTE increased more than 2-fold within 1 month of discharge after surgery (HR = 2.2; 95% CI, 1.4-3.4) compared with patients who did not undergo surgery, but not in other pre- or postoperative time periods. The highest absolute incidence of VTE arose during chemotherapy and one month after chemotherapy cessation and was more than 10.8-fold and 8.4-fold higher than in women not receiving chemotherapy, respectively. The risk of VTE was higher in women not actively receiving chemotherapy with metastatic tumors, although this finding was observed in only 1/3 of the cohort and complete staging information was lacking. Women treated with tamoxifen had a 5.5-fold increased risk of VTE during the first 3 months of treatment compared with the pretreatment period, and the risk continued to rise after 3 months of treatment (HR = 1.9; 95% CI, 0.9-4.3). In contrast, the use of aromatase inhibitors was not significantly associated with a change in VTE incidence. Despite the association of morbidity and mortality with VTE in cancer patients, current clinical practice guidelines do not recommend routine thrombosis prophylaxis in cancer outpatients. The relatively low OR of VTE in breast cancer patients, <1% /year in this study, does not justify that widespread thromboprophylaxis in the population leads to a risk of treatment-related serious adverse effects such as major bleeding. An important challenge is to identify who from moderate to high risk VTE patients is most likely to benefit from initial thromboprophylaxis. The trial evaluating AVE5026 for VTE prevention in cancer patients receiving chemotherapy demonstrated greater efficacy (placebo: nearly 3-fold increased risk of VTE vs. semuloparin treatment), but a smaller absolute risk reduction of 2.2% for VTE (3.2% in the control group and 1.4% in the treatment group). Assuming a 1% risk of intracranial hemorrhage, an absolute risk reduction of this magnitude is not sufficient to offset potential treatment-related harms. In contrast, patients with advanced pancreatic cancer selected for the Charité éonkologie (CONKO)-004 trial had malignancy associated with a high incidence of VTE and showed a clinically meaningful absolute reduction in the risk of VTE - 15.1% of control patients vs. 6.4% of patients in the treatment group. Although VTE is relatively rare, breast cancer is the most common cancer in women worldwide. Therefore, the question of whether to use thromboprophylaxis to reduce VTE associated with breast cancer has significant clinical implications. the results of the Walker et al. study suggest that thromboprophylaxis in breast cancer patients should be targeted to those at highest risk for time-limited therapy. Selective thromboprophylaxis in patients at highest risk, along with the critical importance of using it only when patients are at risk, may limit overtreatment in patients with low benefit and avoid most adverse outcomes. Recognizing the time-sensitive nature of VTE risk associated with surgery and treatment can be used to improve risk prediction algorithms to better identify individuals at risk for thrombosis. Further research is needed on how these results can be used to more precisely target patients for maximum opportunity benefit. Female breast cancer patients undergoing surgery, chemotherapy, or endocrine therapy have a specific period of increased risk for VTE. Therefore, a discussion of common VTE symptoms should include vigilance for neutropenic fever and more common treatment side effects such as rare, highly morbid potential complications of treatment.