The ability of school students to use health-related knowledge for their and their community's needs is referred to as health literacy and is regarded as a combination of knowledge and motivational factors. In the case of cancer literacy, high-school students have some knowledge about risk factors, but not much is known about their understanding of the mechanisms by which these risk factors cause cancer. In addition, motivational factors, such as psychological perceptions of cancers, are not well-characterised in this population. Hence, data are insufficient to support the development of educational programmes for enhancing cancer literacy. We characterised 10th-grade students' knowledge and illness perceptions using open questions and Brief Illness Perception Questionnaire and searched for an association between the two. We found that students have much more causal knowledge than mechanistic knowledge about cancer. We also found that the ability to reason about the mechanisms by which cancer develops is associated with the perceived severity of the disease. Thus, the mechanisms leading to cancer should be taught rather than focusing on risk factors. This study also provides evidence for a possible interplay between a specific type of knowledge (mechanistic) about a given phenomenon (cancer) and psychological perceptions of that phenomenon.