Malignant neoplasms in people with hypothyroidism in Spain: A population-based analysis

PURPOSE: The objective of this study was to determine the association between hypothyroidism and overall and site-specific cancer in Spanish population. METHODS: A cross-sectional study was performed using the population-based database BDCAP (Base de Datos Clínicos de Atención Primaria, primary care clinical database) to analyze the relative risk of cancer in Spanish population with hypothyroidism. RESULTS: In a total of 2,414,165 patients diagnosed with hypothyroidism in BDCAP in 2019, the relative risk (OR) of cancer, compared to the non-hypothyroid population, was 1.73 (1.72–1.74) (P<0.0001). The higher risk was observed in both men (OR 2.15 [2.13–2.17]; P<0.0001) and women (OR 1.67 [1.636–1.68]; P<0.0001). However, hypothyroid persons aged 65 years or older had a reduced risk of cancer (OR 0.98 [0.97–0.98]; P<0.0001). In addition, hypothyroid patients aged 65 or over showed a decreased risk of cancers of the bladder, colorectal, gastric, pancreatic and prostate. Socioeconomic characteristics such as income level, municipality size, country of birth and employment situation had limited influence on the association between hypothyroidism and cancer. However, hypothyroid patients receiving replacement therapy exhibited higher cancer risk compared with patients without treatment (OR 1.30 [1.28–1.31]; P<0.0001). CONCLUSION: Spanish hypothyroid patients of both genders have a risk of overall cancer higher than that found in non-hypothyroid population. However, people over 65 years have a reduced risk of various malignancies. This peculiarity of hypothyroidism should be considered by the health authorities.