Thomboembolic Events in Patients with Breast Cancer: A Population Based Study.

BACKGROUND: Thromboembolic events (TEEs) are common in patients with cancer. Metastatic disease, treatment and comorbidities have been associated with increased risk. In this population-based study we sought to evaluate the risk factors and the prevalence of different TEEs in patients with breast cancer. METHODS: Retrospective cohort study using the SEER-Medicare linked database. Patients with breast cancer (stage I-IV) diagnosed from 1992-2002, who were 66 and older, and had full coverage of Medicare A and B were identified. ICD-9, HCPCS codes were used to identify different TEEs that occurred within one year of the breast cancer diagnosis. We identified pulmonary embolism (PE), deep venous thrombosis (DVT)/thrombophlebitis, other TEEs, as well as the use of chemotherapy, radiotherapy, surgery and comorbidities. Analyses were conducted using descriptive statistics and logistic regression. RESULTS: 71,864 patients were included. Age groups were distributed as follows: 66-70 (24.1%), 71-75 (26.4%), 76-80 (23.2%), >80 (26.3%). At diagnosis 52.4% of patients had stage I, 35.2% stage II, 6.6% stage III and 5.8% stage IV. 66.8% of the patients had ER-positive breast cancer. Within one year of diagnosis, 2652 (3.7%) of patients developed a TEE, including 800 patients with at least two events. 3565 total number of events were observed. A total of 596 (0.85%) PEs, 1252 (1.74%) DVT/thrombophlebitis, and 1717 (3.39%) other TEEs were identified. In the univariate analysis race, marital status, education and poverty level, geographical location, stage, tumor grade, estrogen receptor status, comorbidities, as well as surgical modality, radiation therapy and chemotherapy use, were associated with the development of any TEE.After adjusting for potential confounders, the development of any TEE was associated with ER-positive tumors (OR 1.20, 95% CI 1.07-1.34), stage II vs. I (OR 1.22, 95% CI 1.11-1.35), stage III vs. I (OR 1.63, 95% CI 1.40-1.90), stage IV vs. I (OR 2.16, 95% CI 1.82-2.57), chemotherapy (OR 2.02, 95% CI 1.82-2.23), radiotherapy (OR 1.39, 95% CI 1.27-1.52), comorbidity score (OR 1.19, 95% CI 1.08-1.32 and OR 1.74, 95% CI 1.54-1.96 for score 1 and 2 respectively), and type of surgery (OR 1.25, 95% CI 1,13-1.38 for mastectomy vs. breast conservation surgery and OR 1.23, 95% CI 1.02-1.49 for no surgery vs. breast conservation surgery). Borderline association was seen with age (using 66-70 as a reference value, the ORs for the 71-75, 76-80 and >80 year old categories were: 1.14, 95%CI 1.02-1.28; 1.17, 95% CI 1.04-1.32; and 1.15, 95% CI 1.01-1.29 respectively). Relatively similar estimates were seen for the analysis of PE, DVT/thrombophlebitis and other TEEs. CONCLUSION: 3.7% of patients in this cohort developed a TEE within one year from breast cancer diagnosis. Age, stage, type of treatment, comorbidities and receptor status were associated with the development of TEEs. To the best of our knowledge this is the largest cohort of patients older than 66years old, in which the patterns and risk factors associated with TEEs are analyzed. Whether these observations apply to patients younger than age 65, remains to be established. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 2053.