Different Anatomic Distribution in Men and Women
Men were found to have a greater prevalence of melanocytic nevi and melanoma on the trunk in numerous reports, while women showed a predilection for the extremities, mainly the lower limbs.[41,42,43,44,45,46,47,6,7,8,9] In the 6-9-year age group the mean nevi count was higher on the torsos of boys and on the lower legs of girls, and these differences became more pronounced with age. Different sun exposure stemming from different clothing and recreational habits of men and women is usually held responsible for these patterns.[44,46,47,48] Melanocytic nevi increase in the second life decade; mean nevus count for all body sites until the age of 16 years tend to be greater for boys, while above 16 years of age women had more nevi on the extremities.
Studies among 6-15-year-old white children from Hutterite colonies in Canada[49,50] contradicted these assumptions. In this society, where traditional dress provides near maximal sun protection, the boys had more nevi on the face and on the front and back of the torso, while the girls had more nevi on the upper and lower limbs, as a whole and at each age, even as early as 6 years of age.
The finding of differences as early as 6 years of age reduces the likelihood that the anatomic distribution of nevi is influenced by sex hormones. On the other hand, the increase in the number of nevi during the second decade of life can be attributed at least in part to sex hormones. A possible theory, yet unproved and unexplained, is a regional difference in the tendency of men and women to develop nevi.
The fact that two of the favorable prognostic indicators for melanoma survival -- extremity location and female gender -- usually pertain to the same group raises the question of whether they are independent indicators or are associated. Anatomic location was found to be one of the dominant prognostic factors, whereas gender correlated with survival to a lesser extent. Another study held one of these two prognostic factors stable and allowed the other to vary, assuming the free variable would independently account for the effect on survival. For all melanoma lesions, regardless of location, women had a better survival rate; however, changing the free parameter yielded different results. For women, there was no significant difference in survival according to location of the lesions, while for men there was only a statistically insignificant trend toward improved survival when the lesion(s) was on an extremity. These authors concluded that gender is a significant prognostic factor of survival, independent of any other factor including anatomic location. The anatomic location of the lesion was found to be an independent prognostic parameter, albeit weaker than gender.
Melanoma of the vulva is seen in about 10% of all vulvar malignancies and accounts for 1%-4% of all malignant melanoma.[53,54,55] The incidence of vulvar melanoma in Sweden decreased from 0.27 per 100,000 in 1960 to 0.14 in 1984. The incidence of vulvar and vaginal melanoma in the United States from 1973-1987 was 0.108 and 0.026, respectively, per 100,000 per year, with no increase or decrease during the 15-year period. Median age at diagnosis was 66 years (range, 10-96 years) in the American study vs. 59.4 years (range, 18-92 years) in Germany. The 5-year survival rate ranged from 28% up to 50% for vulvar melanoma and 19% for vaginal melanoma.[53,54,55] Some investigators reported the primary anatomic sites of vulvar melanoma to be the clitoral area (30.8%), labia majora (27.3%), labia minora (19.2%), periurethral area (11.3%), and vagina (4%), while others reported labia minora (80%), labia majora (13%), and clitoris (7%).
The rare melanoma of the penis accounts for no more than 0.2% of all malignant melanoma, and less than 2% of all penile primary malignant tumors.[59,60] Penile melanoma usually occurs in the sixth and seventh decades. The glans penis (55%), prepuce (28%), penile shaft (9%), and urethral meatus (8%) are the most affected sites. This rare melanoma has a dismal prognosis, with life expectancy usually not exceeding 3 years. One study reported inguinal lymph node enlargement detected in 43% of patients suffering from penile melanoma. The high percentage of metastases can be explained by the fact that the penile shaft has no subcutaneous fatty tissue and is rich in lymphatic vessels.
Skinmed. 2003;2(3) © 2003 Le Jacq Communications, Inc.
Cite this: Malignant Melanoma: It Pays to Be a Woman - Medscape - May 01, 2003.