# Prospective associations of leucocyte subtypes and obesity with the risk of developing cutaneous malignant melanoma in the UK Biobank cohort

## TL;DR

Higher monocyte counts and abdominal obesity are linked to lower melanoma risk, while general obesity in men increases it, according to a large study.

## Contribution

This study identifies monocyte count and ABSI as novel prospective predictors of melanoma risk with sex-specific patterns.

## Key findings

- Monocyte count was inversely associated with melanoma risk in older participants and those with higher BMI or low ABSI.
- BMI was positively associated with melanoma risk in men but not women.
- ABSI showed an inverse association with melanoma risk in pre-menopausal women and men.

## Abstract

Obesity is associated with chronic low-grade inflammation, which is linked to cancer development. Abdominal obesity (a body mass index, ABSI), however, has unusually been associated inversely with cutaneous malignant melanoma (CMM), while general obesity (body mass index, BMI) is associated positively. Leucocytes participate in inflammation and are higher in obesity, but prospective associations of leucocytes with cutaneous malignant melanoma are unclear.

We examined the prospective associations of neutrophil, lymphocyte, and monocyte counts (each individually), as well as the prospective associations of ABSI and BMI, with cutaneous malignant melanoma in UK Biobank. We used multivariable Cox proportional hazards models and explored heterogeneity according to sex, menopausal status, age (≥ 50 years at recruitment), smoking status, ABSI (dichotomised at the median: ≥73.5 women; ≥79.8 men), BMI (normal weight, overweight, obese), and time to diagnosis.

During a mean follow-up of 10.2 years, 2174 CMM cases were ascertained in 398,450 participants. There was little evidence for associations with neutrophil or lymphocyte counts. Monocyte count, however, was associated inversely in participants overall (HR = 0.928; 95%CI: 0.888–0.971; per one standard deviation increase; SD = 0.144*109/L women; SD = 0.169*109/L men), specifically in older participants (HR = 0.906; 95%CI: 0.862–0.951), and more clearly in participants with low ABSI (HR = 0.880; 95%CI: 0.824–0.939), or with BMI ≥ 25 kg/m2 (HR = 0.895; 95%CI: 0.837–0.958 for overweight; HR = 0.923; 95%CI: 0.848–1.005 for obese). ABSI was associated inversely in pre-menopausal women (HR = 0.810; 95%CI: 0.702–0.935; SD = 4.95) and men (HR = 0.925; 95%CI: 0.867–0.986; SD = 4.11). BMI was associated positively in men (HR = 1.148; 95%CI: 1.078–1.222; SD = 4.04 kg/m2). There was little evidence for heterogeneity according to smoking status. The associations with monocyte count and BMI were retained to at least 8 years prior to diagnosis, but the association with ABSI was observed up to 4 years prior to diagnosis and not for longer follow-up time.

Monocyte count is associated prospectively inversely with the risk of developing CMM in older individuals, while BMI is associated positively in men, suggesting a mechanistic involvement of factors related to monocytes and subcutaneous adipose tissue in melanoma development. An inverse association with ABSI closer to diagnosis may reflect reverse causality or glucocorticoid resistance.

The online version contains supplementary material available at 10.1186/s12885-024-12344-0.