Phenotypic variation in colorectal adenoma/cancer expression in two families: hereditary flat adenoma syndrome

Article Abstract:

Familiar adenomatous polyposis (FAP) was the first colorectal cancer found to be inherited. The disorder accounts for about one percent of all colorectal cancer. More recently hereditary nonpolyposis colorectal cancer (HNPCC) has been found to involve a dominantly inherited predisposition to the early development of colorectal cancer. This form of familial colorectal cancer is far more common than familial adenomatous polyposis, and may account for more than six percent of all colorectal cancers. Familial adenomatous polyposis has been found to be linked to the long arm of chromosome 5, but the genetic linkage of hereditary nonpolyposis colorectal cancer has not yet been identified. Now, however, two families have been identified in which an inherited syndrome of adenomas and colorectal cancer does not fall into either of these classifications. The average age of cancer onset within these two families is 57 years, in contrast to 40 years for familial adenomatous polyposis and 45 years for hereditary nonpolyposis colorectal cancer. The histologic appearance of the adenomas is flat, in contrast to the tubular adenomas seen in the previously identified syndromes. (Flat refers to essentially horizontal rather than vertical growth of the tumor.) The polyp and cancer distribution is largely on the right side, which resembles HNPCC, but the number of observed polyps is generally between HNPCC and (that is, more than 10, but less than 100 polyps, respectively). The cancer syndrome in these two families appears to be transmitted as an autosomal dominant trait (not sex-linked), and the authors suggest that it may represent an intermediate cancer, between HNPCC and FAP. Preliminary genetic linkage studies are consistent with a linkage of this newly identified colorectal cancer syndrome to the FAP locus on chromosome 5. However, the lod score of 2.7 may be regarded only as suggestive, and not conclusive of this genetic linkage. (Lod refers to the log of the odds ratio; a score of four or greater is generally accepted as indicative of genetic linkage.) (Consumer Summary produced by Reliance Medical Information, Inc.)

Identification and classification, Adenoma

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Hereditary ovarian cancer: heterogeneity in age at diagnosis

Article Abstract:

Little is known about the contribution of genetic factors to the development of ovarian cancer. While the majority of ovarian cancer cases occur sporadically, the disease may also occur within families. There is some indication that ovarian cancer may be transmitted as an autosomal dominant trait in these families. However, not all families in which ovarian cancer occurs are comparable. In some families, the hereditary cancer is specific for the ovary. However, other families may carry the breast-ovarian cancer syndrome. Still other families carry Lynch syndrome II, in which ovarian cancer is associated with hereditary nonpolyposis colorectal cancer. The authors have compared the features of ovarian cancer in a collection families representing each of these three familial ovarian cancer syndromes. Pathological examination did not reveal any characteristics that distinguished the hereditary cancers from the sporadic neoplasms. However, a difference in the age of onset was observed. The average (mean) age of onset for ovarian cancer in the general population is 59 years; the median age is 60 years. For 52 patients with hereditary breast-ovarian cancer in this study, the mean age at diagnosis was 52 years. For the 15 cases of Lynch syndrome II, which were included in the statistical analysis, the mean age at diagnosis was 45 years. A mean age at diagnosis of 49 years was observed for the patients with site-specific familial ovarian cancer. While the age at diagnosis for the three familial cancer syndromes was significantly less than for the population as a whole, the differences among the three syndromes were only marginally significant. Nevertheless, these differences suggest that various mechanisms may be responsible for the development of ovarian cancer. (Consumer Summary produced by Reliance Medical Information, Inc.)

Statistics, Breast cancer, Ovarian cancer

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Genetic diagnosis of Lynch syndrome II in an extended colorectal cancer-prone family

Article Abstract:

Most physicians are aware of familial polyposis syndrome, or familial adenomatous polyposis, as a genetic risk factor for colorectal cancer. However, many mistakenly believe that it is the only genetic predisposition to colon cancer. In reality, familial polyposis accounts for only about one percent of colorectal cancer, while hereditary nonpolyposis syndromes may be from six to eight times more common. Two major nonpolyposis syndromes, which the authors refer to as Lynch syndromes I and II, may be recognized by careful evaluation of the family history, but the authors feel that inadequate attention is given to this by the majority of physicians. They illustrate this point by recounting the diagnosis of Lynch syndrome II in an extended kindred in a midwestern community. Lynch syndrome II involves not only cancer of the colon and rectum, but also of the endometrium and ovaries as well. Despite the regular occurrence of these tumors over five generations, the syndrome was not recognized in this kindred due to scant attention paid to the family history. Lynch syndrome II is also distinguished by the early onset of the cancer and the proximal predominance of adenocarcinoma of the colon. The syndrome is inherited as an autosomal dominant trait. The authors point out that no known cancer risk factor is greater than the roughly 50 percent risk carried by a first-degree relative of a patient with autosomally dominant inherited colorectal cancer. Nevertheless, within the current preoccupation with dietary factors, many physicians continue to give short shrift to the family history in cases of colorectal cancer. (Consumer Summary produced by Reliance Medical Information, Inc.)

Diagnosis, Polyposis, Familial, Familial polyposis

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