CCNA1 and cancer: After excluding the duplicates (n = 2), letters, reviews, or meta-analyses (n = 9), nonhuman studies (n = 13), and the studies not related to research topics (n = 20), the remaining studies (n = 36) were reviewed and additional 23 studies were excluded for not being case-control or cohort study (n = 4), relevant to CCNA1 (n = 7), or relevant to cancer (n = 12).