Also known as octyl methoxycinnamate or ethylhexyl methoxycinnamate, octinoxate is the oldest and most common sunscreen active used to protect skin against primarily UVB rays. While octinoxiate does provide some degree of UVA protection, it can't do it all on its own and so you'll want to see another UVA active present in any sunscreen you use. It has a solid record of safety (decades of research and thousands of studies establishing its safety in sunscreens as indisputable), Unfortunately, unfounded claims that this staple of SPF formulas "causes cancer" have made many afraid of their sunscreens.
Let's be clear: no studies demonstrate octinoxate when used in your SPF products causes, or increases the risk for developing cancer. In the sole studies cited when the "octinoxate = cancer" claim is made, the conditions are completely inapplicable to how sunscreens ingredients are used in skin-care products.
For example, such studies use octinoxate in high concentrations (much higher than would ever be used in sunscreens) applied directly to skin cells, or fed in high concentrations to lab animals. The moral here is that octinoxate is safe as long as you aren't drinking it!
Conclusion: No studies exist that back the claim octinoxate has any link to causing cancer or other illnesses when used in sunscreen formulas. In fact, the EU's usage level for octinoxate in sunscreens is higher than what is permitted in the United States (7.5% in the US vs. 10% in the EU).
Sources: Pharmazie, January 2013, pages 34-40; Skin Pharmacology and Physiology, July-August 2005,pages 170-174; and http://www.skininc.com/skinscience/ingredients/160839235.html.