A NEW CATEGORY OF CANCERS FOUND
BAR HARBOR, Me., July 23— Scientists are searching for more cases of a newly discovered category of cancers that arise because of the loss of normal genes, according to a report here today.
Such cases have been found recently in two types of rare hereditary cancers of children, the scientific evidence indicates. These are retinoblastoma, a hereditary cancer of the eyes, and Wilms tumor, a cancer that strikes the kidneys.
Specialists have now begun to search for comparable cases in many other kinds of cancer, including some known to be strongly influenced by hereditary predisposition, according to Dr. Webster Cavenee of the University of Cincinnati. As examples worth exploring, he cited breast cancer and cancer of the colon, both common among Americans.
There is evidence that hereditary predisposition is a factor in both kinds of cancers, although evidently to a far lesser extent than is true of retinoblastoma and Wilms tumor.
The fundamental cause of most human cancers is unknown, but much recent scientific interest has focused on evidence suggesting that certain genes can be activated abnormally to start the complex process of malignancy. Mechanism in Cancer Cases
The new research described today suggests a sharply different mechanism for some cancers – that they arise when key normal genes are missing or inactivated.
Dr. Cavenee and two colleagues at the University of Cincinnati, Dr. Neal G. Copeland and Dr. Nancy A. Jenkins, spoke at a briefing for science reporters held as part of a special two-week course on the medical and mammalian genetics conducted by faculty members of Johns Hopkins University, the Jackson Laboratory here and other invited speakers.
The course, sponsored here annually for 25 years by the March of Dimes Birth Defects Foundation, is attended by physicians and scientists from many laboratories in the United States and elsewhere.
Study of genetic material from children suffering from retinoblastoma and from their parents indicates that some cases of the disease arise only after the loss of normal genetic material on chromosome number 13, said Dr. Cavenee.
In several cases studied, one parent had suffered from retinoblastoma, while the other had not. In the child who developed the disease, the cancerous cells were found to lack a copy of the chromosome from the nonaffected parent and to have two copies of the chromosome inherited from the parent who had developed the cancer.
The evidence suggested strongly that the cancer was able to arise because of the lack of some key genetic material on the chromosome.
The specific genes involved have not yet been identified.
Report on Findings
A report on the retinoblastoma research was published last fall by scientists at the University of Cincinnati, the University of Southern California, Harvard University, M. D. Anderson Hospital in Houston, the University of Toronto and the University of Utah.
Within the past few months, comparable cases have been reported by several institutions in patients suffering from Wilms tumor of the kidney. In these cases, chromosome 11 rather than 13, was involved. The discoveries concerning Wilms tumor included research at University of Cincinnati, Johns Hopkins and Children’s Hospital in Boston.
Some patients treated successfully for retinoblastoma by surgical removal of the tumors later developed other cancers, including osteosarcoma, which affects the bone, Dr. Cavenee said.
The evidence suggests that the same mechanism that led to the retinoblastoma was also involved in the osteosarcoma. Comparable patients with Wilms tumor seemed predisposed to later development of cancer of the liver or leukemia.
Both in the cases of retinoblastoma and Wilms tumor, the likelihood that a child will develop such disease can be determined early in the pregnancy by means of amniocentesis, a procedure in which the amniotic fluid of a pregnant woman is analyzed, although only a very few cases have been tested this way to date, Dr. Cavenee said.