Abstract P2-09-13: Adverse events rates in a privately insured US population on tamoxifen compared to controls from the MarketScanR database
Authors: Peterson LL , Simpson KN 
Published: March 2017

Patients with breast cancer (BC) and those at high risk for BC are often reluctant to initiate Tamoxifen (Tam) due to potential adverse events (AEs) such as deep vein thrombosis (DVT), pulmonary embolus (PE), acute ischemic stroke (AIS), myocardial infarction (MI) and endometrial cancer (EC). Some decline this life saving therapy due to fear of AEs. AE rates from RCTs are low, but AE rates in the general population are not well documented.

Methods: The MarketScanR database (2010-2013) was searched for patients aged 30-64 with a prescription of Tam active for more than 120 days. Patients with prior DVT, PE, AIS, MI or EC were excluded. ICD-9 codes for DVT, PE, AIS, MI and EC for inpatient and outpatient encounters were used to determine the frequency of AEs while on Tam. Patients taking Tam for prevention, DCIS or invasive cancer were included. Results were stratified by sex, age and time on Tam (in years). A random control group was created from the database utilizing patients age 30-64 with a levothyroxine prescription active for more than 120 days to calculate odds ratios (OR) for the AEs.

Results: 67,887 patients on Tam, including 1622 males, were analyzed, for a total of 93,498 Tam Exposure Years. The control group included 2.4 million patients. The average age of Tam users was 48 (males), 50 (females). The average age of controls was 51 (males), 50 (females). Ages (%) represented in Tam users: 30-34 (2%), 35-44 (20%), 45-54 (52%), 55-64 (26%). The average time on Tam was 1.4 years for females, 1.0 years for males (.33-4.2). DCIS accounted for 17% of Tam use, &lt;1% was for prevention. AE rates and odds ratios (OR) are in the table below.

Adverse Events Rate and Odds Ratios AE% TAM usersAE% ControlsOR (95% CI)AE% in 55-64 Year OldsAE% in 30-54 Year OldsOR Male v FemaleOR &gt;2 Yrs TAM use vs.&lt; 2 Yrs TAM useDVT1.420.722.37 (2.22-2.53)1.701.321.301.07PE0.870.432.37 (2.17-2.58)1.120.781.331.12AIS0.510.700.89 (0.80-.099)0.830.401.251.16MI0.370.700.80 (0.70-.090)0.600.302.851.22EC0.900.293.03 (2.78-3.29)1.520.68N/A0.99 **Not statistically significant

Conclusions: Despite an increased odds of DVT, PE and EC, AE rates in patients on Tam are remarkably low, especially in the younger age population, the population most likely to be on Tam. The odds of AIS and MI are lower in Tam users than controls. The favorable risk/benefit profile of this drug should be emphasized to patients who would benefit from its use, with the use of actual event rates, not odds ratios, being the focus of discussion with patients. Male sex increases the odds of DVT, PE, AIS and MI. Increasing age and use of Tamoxifen for more than 2 years increase the odds of having an AE. Further analysis will evaluate whether there are differences in AE rates between Tamoxifen patients based on their diagnosis (prevention, DCIS, invasive cancer).

Citation Format: Peterson LL, Simpson KN. Adverse events rates in a privately insured US population on tamoxifen compared to controls from the MarketScanR database [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-09-13.