Background: Abnormally low plasma levels of coenzyme Q10 (CoQ10) have been found in patients with cancer of the breast, lung, or pancreas. Objective: A prospective study of patients with melanoma was conducted to assess the usefulness of CoQ10 plasma levels in predicting the risk of metastasis and the duration of the metastasis- free interval. Methods: Between January 1997 and August 2004, plasma CoQ10 levels were measured with high- performance liquid chromatography in 117 consecutive melanoma patients without clinical or instrumental evidence of metastasis according to American Joint Committee on Cancer criteria and in 125 matched volunteers without clinically suspect pigmented lesions. Patients taking CoQ10 or cholesterol- lowering medications and those with a diagnosis of diabetes mellitus were excluded from the study. Multiple statistical methods were used to evaluate differences between patients and control subjects and between patients who did (32.5% ) and did not (67.5% ) develop metastases during followup. Results: CoQ10 levels were significantly lower in patients than in control subjects (t test: P< .0001) and in patients who developed metastases than in the metastasis- free subgroup (t test: P< .0001). Logistic regression analysis indicated that plasma CoQ10 levels were a significant predictor of metastasis (P=.0013). The odds ratio for metastatic disease in patients with CoQ10 levels that were less than 0.6 mgL (the low- end value of the range measured in a normal population) was 7.9, and the metastasis- free interval was almost double in patients with CoQ10 levels 0.6 mgL or higher (Kaplan- Meier analysis: P<.001). Limitations: A study with a larger sample, which is currently being recruited, and a longer follow- up will doubtlessly increase the statistical power and enable survival statistics to be obtained. Conclusions: Analysis of our findings suggests that baseline plasma CoQ10 levels are a powerful and independent prognostic factor that can be used to estimate the risk for melanoma progression. Background: Abnormally low plasma levels of coenzyme Q10 (CoQ10) have been found in patients with cancer of the breast, lung, or pancreas. Objective: A prospective study of patients with melanoma was conducted to assess the usefulness of CoQ10 plasma levels in predicting the risk of metastasis and the duration of the metastasis-free interval. Methods: Between January 1997 and August 2004, plasma CoQ10 levels were measured with high- performance liquid chromatography in 117 consecutive melanoma patients without clinical or instrumental evidence of metastasis according to American Joint Committee on Cancer criteria and in 125 matched volunteers without clinically suspect pigmented lesions. Patients taking CoQ10 or cholesterol- lowering medications and those with a diagnosis of diabetes mellitus were excluded from the study. Multiple statistical methods were used to evaluate differences between patients and control subjects and between patients who did (32.5%) and did not (67.5%) devel Results: CoQ10 levels were significantly lower in patients than in control subjects (t test: P <.0001) and in patients who developed metastases than in the metastasis-free subgroup (t test: P <.0001). Logistic regression analysis showed that plasma CoQ10 levels were a significant predictor of metastasis (P = .0013). The odds ratio for metastatic disease in patients with CoQ10 levels that were less than 0.6 mgL (the low-end value of the range measured in a normal population) was 7.9, and the metastasis- free interval was almost double in patients with CoQ10 levels 0.6 mgL or higher (Kaplan-Meier analysis: P <.001). Limitations: A study with a larger sample, which is currently being recruited , and a longer follow- up will doubtlessly increase the statistical power and enable survival statistics to be obtained. Conclusions: Analysis of our findings suggests that baseline plasma CoQ10 levels are a powerful and independent prognostic factor that can be usedto estimate the risk for melanoma progression