GENETICS IN GYNECOLOGY: CANCER SCREENING
It is now
known that certain breast and ovarian cancers have a genetic predisposition.
Genetic tests have been developed for the detection of some of these genes. Gynecologists
play a key rolein identifying individuals with a genetic disposition for
can-cer and ensuring that they receive the appropriate screen-ing tests. The
most important initial step in identifying women at high risk for hereditary
cancers is a thorough family history. Clues to possible hereditary cancers
include a history of cancers in first-degree relatives, cancers occur-ring at
young ages, cancers in multiple generations, or many different cancers in one
individual. Based on these findings, further testing and genetic counseling may
be indicated.
The BRCA1 and BRCA2
genes have been identified as responsible for the hereditary forms of both
breast and ovarian cancers. Clinically important BRCA mutations have been found in about 2% of Ashkenazi Jewish
women, and are estimated to occur in about 1 in 300 to 500 women in the general
non-Jewish US population. Criteria devel-oped by the U.S. Preventative Services
Task Force for BRCA testing referral
are as follows:
· Two first-degree
relatives with breast cancer, with at least one diagnosed at under age 50
· Three or
more first-degree or second-degree relatives with breast cancer at any age
· A
first-degree or second-degree relative with breast and ovarian cancer
· Two or
more first-degree or second-degree relatives with ovarian cancer
· A male
relative with breast cancer
Because the incidence of breast
cancers linked to BRCA is higher in
Ashkenazi Jewish women, the testing criteria for them are slightly different.
Testing for BRCA in this population is indicated if the following are present:
· Any
first-degree relative with breast or ovarian cancer
·
Two second-degree relatives on
the same side of the family with breast or ovarian cancer.
In addition to breast cancer, other cancers
have been found to have a hereditary component. A hereditary syndrome called
hereditary nonpolyposis colorectal cancer type A (HNPCC type A), or Lynch I
syndrome, increases therisk for developing colon cancer. A family history
of colon, endometrial, ureteral, or renal cancers should alert the clinical to
screen for the HNPCC-linked genes. HNPCCtype
B, or Lynch II syndrome, is an
autosomal dominantinherited syndrome that increases the risk for all of the
cancers in Lynch I syndrome, as well as for ovarian, gastric, and pancreatic
cancers. Individuals or families who meet certain criteria, which include the
presence of HNPCC in two successive generations and the diagnosis of HNPCC in
at least three relatives, can undergo genetic testing to determine whether they
have the defective gene.
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