This article investigates the coverage of different types of cancer on two major social networks sites, Facebook and Instagram. A categorical content analysis is performed on a corpus of 2,446 posts collected via a web listening tool on these two social media. The primary objective is to assess the coverage of different types of cancer on these social media. The second objective is to detect any distortions between this social media coverage and the number of new patients (incidence rate) in French-speaking countries of the West in 2020. Our results highlight the predominance of breast cancer coverage (18.3%), pediatric cancer (9.7%), leukemia (4.2%), but also the over-representation of female cancers accompanied by an under-representation of male cancers and urological cancers. Insofar as the efforts of groups defending certain diseases create a considerable impact on social media— and subsequently on the public agenda — it is of paramount importance to draw the attention of policymakers, scientists, and organizations on these representation gaps (distortions), by further engaging, for instance, communities around less visible cancers.