Although nevi are considered among the strongest risk factors for melanoma, most patients with melanoma had few total nevi and no atypical nevi, according to an analysis of 566 patients with invasive cutaneous melanoma. “Three notable findings emerged from this case study,” Alan C. Geller, MPH, RN, of the Harvard T.H. Chan School of Public Health, Boston, and colleagues wrote in JAMA Dermatology.
“First, overall, most patients had 0 to 20 total nevi and no atypical nevi, and this finding was most pronounced among older patients, for whom both total nevi and atypical nevi were uncommon. Second, after controlling for potential confounders, a higher mole count (> 50 total nevi) was associated with thinner melanoma (≤ 2.00 mm) for those younger than 60 years. Third, paradoxically, the presence of more than five atypical nevi was associated with thicker melanoma for patients younger than 60 years.”
All patients were 18 years or older, and the mean age was 56.7 years. Age “was dichotomized as younger than 60 years vs 60 years or older, given increasing rates of thicker tumors and increased mortality among older individuals,” the authors explained. “Tumor thickness was categorized as 2.00 mm or less or as 2.01 mm or greater.”
The patients were surveyed within 3 months of diagnosis at the University of Michigan, Ann Arbor, and at Stanford University Medical Center and the Veteran Affairs Palo Alto Health Care System, California. In addition to information about age, sex, race/ethnicity, and marital or cohabitation status, patients were asked about skin self-examination, skin examination by a physician, how the melanoma was discovered, and the number of health-care visits during the previous year.
At the first visit following diagnosis, two experienced pigmented lesion specialists “counted the number of total nevi and atypical nevi using established guidelines, based on size (generally > 6 mm), color (variegation), topographic asymmetry, dermoscopic features, and overall nevus morphologic structure. All nevi were counted in the total nevus count, regardless of the size, and dermoscopic examination of atypical nevi was standard in these pigmented lesion practices to avoid misclassification of early or evolving melanoma in situ as atypical nevi,” the investigators explained.
Classified by the number of total nevi, 66.4% (n = 376) had 0 to 20 total nevi, 20.5% (n = 116) had 20 to 50 total nevi, and 13.1% (n = 74) had more than 50 total nevi. “Notably, 43.7% (n = 62) of the youngest patients (≤ 45 years) had few total nevi (0–20), and this rate almost doubled for the oldest patients,” the researchers reported. The youngest patients were more likely to have more than 50 total nevi, 28% (n = 40) vs 14.1% (n = 19) for patients 46 to 57 years, 7.5% (n = 11) for patients 58 to 68 years, and 2.8% (n = 4) for patients ≥ 69.
The number of atypical nevi increased with the number of total nevi, but 73.3% (n = 415) had no atypical nevi, 14.5% (n = 82) had one to five atypical nevi, and 12.2% (n = 69) had more than five atypical nevi. The proportion of patients with no atypical nevi ranged from 51.3% (n = 73) of patients ≤ 45 years to 93.0% (n = 133) for patients ≥ 69 years. The proportion of patients with more than five atypical nevi was 26.8% (n = 38) for patients ≤ 45 years, 14.1% (n = 19) for patients 46 to 57 years old, 6.8% (n = 10) for patients 58 to 68 years old, and 1.4% (n = 2) for patients ≥ 69 years old.
“For those younger than 60 years, the presence of more than 50 total nevi was associated with a sharply reduced risk of thick melanoma (odds ratio, 0.32; 95% confidence interval [CI], 0.12–0.81), and the presence of more than five atypical nevi compared with no atypical nevi was associated with thicker melanoma (odds ratio, 2.43; 95% CI, 1.02–5.75),” the researchers reported.
“Several novel public health messages emerge from our study, including that melanomas are more commonly diagnosed in individuals with fewer nevi compared with those with a high mole count. Therefore, physicians and patients should not rely on the total nevus count as a sole reason to perform skin examinations or to determine a patient’s at-risk status,” the authors concluded. “Younger and middle-aged patients with an increased total nevus count have a lower risk of thick melanoma, but this age group has higher rates of thick melanoma if they have more than five atypical nevi. These younger patients should be educated on the increased risk of thicker melanomas that is associated with having more atypical nevi.”