copies of this oncogene. Detecting its amplification or the overproduction of its protein product (a growth factor receptor on the cell surface) may be useful clinically. It may help in determining patient prognosis and in deciding, for example, if adjuvant therapy should be given after surgery.
Since many breast cancers recur even though they have apparently good risk factors—such as small tumor size, positive estrogen receptors or negative lymph node involvement—it is hoped that new tests such as those for the HER-2/neu oncogene will be able to identify women at an exceptionally high risk for recurrence and for whom additional therapy might increase their chances for cure or prolonged survival.
The HER-2/neu oncogene has also been found to be amplified or overexpressed in ovarian, gastric and non-small cell lung cancers. In these cases, there also appears to be a correlation between this abnormality and poor prognosis with increased mortality .
Genetic Losses Recent studies have suggested that one tumor-suppressor gene , p53, found on chromosome 17, is defective or missing in many cases of cancer, including those arising in the breast, colon and bladder. Missing segments of other chromosomes have also been identified, suggesting that other tumor-suppressor genes are abnormal in these three common cancers. Losses on chromosomes 9, 11 and 17 occur in bladder cancers, for example, and losses on chromosomes 3, 6 and 11 occur in ovarian cancer.
These findings support the theory that multiple genetic losses and not just a single gene defect lead to cancer progression .
