SUMMARY: ColoRectal Cancer (CRC) is the third most common cancer diagnosed in both men and women in the United States. The American Cancer Society estimates that approximately 135,000 new cases of ColoRectal Cancer will be diagnosed in the United States in 2016 and over 49,000 patients are expected to die of the disease. Several epidemiological studies as well as randomized controlled trials have shown that Aspirin and NonSteroidal Anti-Inflammatory Drugs (NSAIDs) reduce the incidence of ColoRectal Cancer (CRC) and CRC associated mortality. Nonetheless, use of aspirin for the primary prevention of CRC, is not routinely recommended, for the fear of aspirin-induced gastric and cerebral hemorrhages. Even though the benefits of Aspirin in the primary prevention of CRC remains well established, the role of Aspirin in secondary prevention in patients with CRC (after the diagnosis of CRC) is unclear. Platelets have long been implicated in the mechanism of tumor metastases. More recent data suggests that platelets may play a role in tumorigenesis as well, through the release of angiogenic and growth factors due to overexpression of COX-2. Daily low dose Aspirin inhibits COX-1 and COX-2. It is postulated that Aspirin also works by COX-independent mechanisms such as, the inhibition of NF-kB and Wnt/ β-catenin signaling, which may play a role in its chemopreventive properties.
The authors conducted this trial to evaluate the association between Aspirin use after diagnosis of CRC and CRC-Specific Survival (CSS) and Overall Survival (OS), in the largest group of patients ever studied. The study authors in this retrospective, population-based study identified 24,495 patients in the Cancer Registry of Norway, diagnosed with ColoRectal Cancer from 2004 through 2011 and a total of 23,162 patients diagnosed with CRC were included. Using the Norwegian Prescription Database, the authors were then able to establish that 6,102 patients in this large cohort had documented exposure to Aspirin. Exposure to Aspirin was defined as a prescription for more than 6 months of Aspirin, following a diagnosis of CRC. The median follow up was 3 years.
The authors performed a multivariate regression analysis controlling for age, gender, tumor stage, tumor differentiation and noted that exposure to Aspirin post-diagnosis, independently improved ColoRectal Cancer-Specific Survival (HR=0.85; P<0.001) and Overall Survival (HR=0.95; P<0.076). Patients who used Aspirin both before and after diagnosis of CRC had additional improvement in ColoRectal Cancer-Specific Survival (HR= 0.77; P<0.001) and Overall Survival (HR=0.86; P<0.001). Further, patients with poorly and moderately differentiated tumors experienced the greatest benefits of Aspirin exposure, as well as those with stage II disease. The researchers were also able to demonstrate that Aspirin use was most beneficial in the first 2 to 3 years after diagnosis.
It was concluded that Aspirin use after the diagnosis of ColoRectal Cancer, is independently associated with improved Colorectal Cancer-Specific Survival and Overall Survival. Because of the increased risk for bleeding, the risk-benefit should be assessed before Aspirin is routinely recommended to this patient population. Aspirin as Secondary Prevention in Patients With Colorectal Cancer: An Unselected Population-Based Study. Bains SJ, Mahic M, Myklebust TA, et al. Published online before print May 31, 2016, doi:10.1200/JCO.2015.65.3519JCO May 31, 2016 JCO653519