Increased frequency of LOH on chromosome 9 in sporadic primary melanomas is associated with increased patient age at diagnosis.

We carried out statistical analysis of the frequency of loss of heterozygosity (LOH) at 10 microsatellite markers on chromosome 9. In 44 microdissected sporadic primary melanomas a comparison of LOH frequency data with other patient data, like age at diagnosis and tumour thickness, showed an interesting correlation between patient age at diagnosis and frequency of LOH on chromosome 9. The patient group with age >72 years at diagnosis (n = 22, mean age 82.3 +/- 6.0 years, mean LOH 3.4 +/- 2.3) showed significantly increased LOH frequency (OR 3.1, 95% CI 1.8-5.3; chi(2) test, P < 0.0001) compared with age group </=72 years (n = 22, mean age 56.1 +/- 14.5 years, mean LOH 1.8 +/- 1.7). A statistically significant increased frequency of LOH (OR 3.5, 95% CI 1.5-7.9; chi(2) test, P = 0.03 after Bonferroni correction) was found only at marker D9S736 on 9p22 (telomeric to the INK4-ARF locus) relative to other markers on six different chromosomes. No other marker, including those located within the INK4-ARF locus, showed a statistically significant increased frequency of LOH. Our results for the first time show a non-random tendency for increased allelic loss in melanomas with increased patient age at diagnosis, besides supporting the existence of an additional tumour suppressor gene(s) on chromosome 9.