Correlation between allergy and cancer: a systematic review and meta-analysis

The relationship between allergies and cancer has been a topic of debate for decades. This study conducted a systematic review and meta-analysis of 53 studies to evaluate the association between allergies and cancers. Case-control and cohort studies were analyzed, focusing on cancer incidence. The results showed significant negative correlations between allergies and cancers such as colorectal cancer, lymphoma, pancreatic cancer, leukemia, and brain cancers. For colorectal cancer, the pooled odds ratio (OR) for any allergy was 0.77 (95% CI 0.67-0.87). Asthma was associated with a reduced risk of lymphoma (OR 0.81, 95% CI 0.70-0.94) and gynecological cancers (OR 0.72, 95% CI 0.53-0.97). For Pancreatic cancer, any allergy was associated with an OR of 0.68 (95% CI 0.59-0.77). Hay fever showed a strong inverse association with brain cancer risk (OR 0.66, 95% CI 0.58-0.76). However, atopic allergy was positively linked to an increased risk of lymphoma (OR 2.02, 95%CI 1.10-3.70). The study highlighted significant variations in the effects of different allergy types on cancer risks. These findings suggest that allergies may act as protective factors against certain cancers, while atopic allergy may increase the risk of certain cancers. However, the certainty of evidence, assessed using the GRADE framework, was low to very low, and results should be interpreted with caution. In particular, associations for lung cancer, leukemia, and gastrointestinal cancers were supported by very low-certainty evidence, primarily due to reliance on observational designs, heterogeneity among studies. These findings underscore the complex and heterogeneous relationship between allergies and cancer, and highlight the need for further high-quality research to elucidate the underlying mechanisms and assess clinical implications.