Aspirin is arguably the synthesized drug that has been used most commonly in human history. Aspirin was originally developed and marketed for the treatment of inflammatory disorders at the end of the 19th century, but its mechanism of action remained unknown until the second half of the 20th century. Since the latter part of the 20th century aspirin also has been used for the primary and secondary prevention of cardiovascular diseases given its anti-thrombotic properties. An association between intake of aspirin and decreased cancer risk was identified in the past decades. Whether aspirin can be used as an anticancer agent in patients with a diagnosis of cancer was unknown until recently. Recent studies suggest that aspirin might provide therapeutic benefit in the adjuvant treatment of certain forms of cancer. This review provides a critical update on this topic, which has potential implications for oncologists and their patients.