Mercury (Hg) in biological samples in association with cancer risk and associated mortality: A systematic literature review

Mercury (Hg) is a heavy metal widely present in the environment as a result of its use in several industrial activities. While multiple adverse health effects of exposure to Hg are established, its link to cancer is still controversial. This systematic review aims to summarize the most updated evidence on the association between Hg levels quantified in biological specimens and cancer incidence and mortality, whether overall or site-specific. We reviewed articles published in PubMed and EMBASE until 10th December, 2025 which examined Hg concentration in biological samples (e.g., blood, urine, and finger/toe-nails) in relation to cancer incidence or mortality. Study quality was assessed using the NOS (Newcastle-Ottawa Scale) tool. We included 31 articles published between 2012–2025, including 11 non-nested case-control studies, 4 nested case-control studies, 6 cohort studies, and 10 cross-sectional studies. The association between Hg levels and cancer risk varied according to cancer site and biological matrix. No consistent correlation was found for gastrointestinal, colorectal, pancreatic, breast, cervical, and uterine cancers. Likewise, studies on prostate, bladder, urinary tract, brain, and nervous system cancers mostly reported null results. Suggestive evidence emerged for a link between Hg biological levels and the risk of cancer of the skin and thyroid gland. The findings were predominantly null also for cumulative cancer mortality. The existing studies focusing on the association between Hg in biological samples and cancer risk are still limited in number and do not reveal a clear pattern for any cancer type.