Tetraploidization and progressive loss of 6q in a squamous cell carcinoma of the parotid gland

Cytogenetic analysis of short-term cultures from a squamous cell carcinoma (SCC) of the parotid gland revealed one clone with loss of the Y chromosome only, as well as three related subclones: 91,XXYY,add(6)(q21), −11,add(11)(p11), ins(15;?)(q22;?)[cp5]/91,XXYYadd(6)(q21), −11,add(11)(p11), ins(15;?)(q22;?),der(22)t(11;22)(pl1;q11)[2]/91,XXYYadd(6)(q11), −11,add(11)(p11), ins(15;?)(q22),der(22) t(11;22)(p11;q11) [cp4]. The finding of only one copy of all structurally rerranged chromosomes in a neartetraploid karyotype indicates that tetraploidization was an early event in tumorigenesis. Rearrangements, in particular deletions, of 6q have previously been associated with adenoid salivary gland malignancies. Our finding of progressive 6q loss with clonal evolution, combined with the fact that 6q deletions were also seen in the two previously reported SCCs of the salivary glands, indicate that loss of genetic information from this chromosome arm is characteristic for most types of salivary gland carcinomas, irrespective of their histologic differentiation.