Squamous cell carcinoma of the skin with an unusual marker chromosome.

Chromosome studies were undertaken on uncultured material from a primary anaplastic squamous cell carcinoma of the skin from a female aged 81. The modal chromosome number was 42. Four marker chromosomes were present in most metaphases: a der (1) which resulted in tetrasomy for most of 1q, a giant chromosome consisting of most of a chromosome 2 and 4q, a small metacentric which was probably an isochromosome for 4p or 5p, and a small chromosome, considered to be an 18q+. The latter was conspicuous in unbanded orcein-stained preparations owing to the presence of a virtually nonstaining region on its long arm. These findings are of interest in the light of the paucity of data on this type of tumour.