11p Deletions and breakpoints in squamous cell carcinoma: Association with altered reactivity with the UM‐E7 antibody

The UM‐E7 monoclonal antibody raised against the UM‐SCC‐I human squamous cell carcinoma (SCC) cell line identifies a cell surface antigen that is strongly expressed in normal tissues. The locus (MICI) controlling the expression of E7 and related cell surface antigens has been mapped to chromosome band I I p 13. This band has been identified as a region of cancer‐associated aberrations and as the probable locus of a tumor suppressor gene. Although E7 antigen expression is strong in normal keratinocytes, it varies among squamous carcinoma cell lines. Some SCC lines (12/26) exhibit weak expression of the E7 antigen, whereas other SCC cell lines (14/26) and 21 cell lines from other tumor types express the antigen strongly. On the basis of these observations and of mapping data, we postulated that low E7 antigen expression in a subset of SCC cell lines might be associated with chromosomal rearrangement or deletion involving the E7 locus on 11p. Fully evaluable karyotypes were prepared from 19 SCC cell lines, including I I with weak and eight with strong E7 expression. Eight of the I I lines with weak E7 expression had I I p abnormalities. Four of these contained I I p deletions, and four others had a breakpoint in 11p. In contrast, none of the cell lines in the group with strong E7 expression had an I I p deletion, although one had a rearrangement with an 11p breakpoint. In the four tumors with visible 11p deletions, the smallest region of overlap corresponded to the 11p13‐p14 region. The mean log₁₀ 50% endpoint E7 titer in the group with 11p deletions or breakpoints was nearly two orders of magnitude lower than that of the lines with no 11p abnormality (1.95 ± 0.53) (P < 0.02). Our results indicate that the UM‐E7 antibody identifies tumors with 11p 13‐p 14 deletions and other 11p rearrangements and that the 11p region is a site of nonrandom chromosome rearrangement in a subset of human squamous cancers. The strong association of loss of antigen expression with visible 11 p deletion or rearrangement in some tumors suggests that other tumors with this phenotype may contain submicroscopic lesions of 11 p 13‐p 14.