[Lynch syndrome: genetic, clinical and diagnostic aspects]

This review aims to present the genetic, clinical and diagnostic aspects of Lynch syndrome, as well as providing the most relevant information about genetic counseling in these patients and the current recommendations for their surveillance.

Milestones of Lynch syndrome: 1895-2015

Lynch syndrome, which is now recognized as the most common hereditary colorectal cancer condition, is characterized by the predisposition to a spectrum of cancers, primarily colorectal cancer and endometrial cancer. We chronicle over a century of discoveries that revolutionized the diagnosis and clinical management of Lynch syndrome, beginning in 1895 with Warthin's observations of familial cancer clusters, through the clinical era led by Lynch and the genetic era heralded by the discovery of causative mutations in mismatch repair (MMR) genes, to ongoing challenges.

Review of the Lynch syndrome: history, molecular genetics, screening, differential diagnosis, and medicolegal ramifications

More than one million patients will manifest colorectal cancer (CRC) this year of which, conservatively, approximately 3% (approximately 30,700 cases) will have Lynch syndrome (LS), the most common hereditary CRC predisposing syndrome. Each case belongs to a family with clinical needs that require genetic counseling, DNA testing for mismatch repair genes (most frequently MLH1 or MSH2) and screening for CRC. Colonoscopy is mandated, given CRC's proximal occurrence (70-80% proximal to the splenic flexure). Due to its early age of onset (average 45 years of age), colonoscopy needs to start by age 25, and because of its accelerated carcinogenesis, it should be repeated every 1 to 2 years through age 40 and then annually thereafter. Should CRC occur, subtotal colectomy may be necessary, given the marked frequency of synchronous and metachronous CRC. Because 40-60% of female patients will manifest endometrial cancer, tailored management is essential. Additional extracolonic cancers include ovary, stomach, small bowel, pancreas, hepatobiliary tract, upper uroepithelial tract, brain (Turcot variant) and sebaceous adenomas/carcinomas (Muir-Torre variant). LS explains only 10-25% of familial CRC.

From cancer families to HNPCC: Henry Lynch and the transformations of hereditary cancer, 1975-1999

Hereditary non-polyposis colorectal cancer (HNPCC) helps us understand how medical genetics has changed over the last forty years. The concept of the "cancer family" emerged from the realization that members of some families developed cancer more frequently than members of others, which led to a series of strategies by clinicians in the 1960s to persuade others of this. By the early 1990s molecular genetics had transformed the disease, from one that a few physicians believed ran in families, to one with precise genetic components that researchers generally accepted, and that could be detected through genetic tests. Nevertheless, a diagnosis of HNPCC still requires that the mutated genes be found within a kin group that is generally accepted as a cancer family. Moreover, the "cancer family" construct was crucial in the search for the HNPCC genes. HNPCC's trajectory can be mapped onto important debates about the complex relations between clinical and molecular genetics knowledge and practice.

History and molecular genetics of Lynch syndrome in family G: a century later

CONTEXT

In 1895, Aldred Scott Warthin, MD, PhD, initiated one of the most thoroughly documented and longest cancer family histories ever recorded. The unusually high incidence and segregation of cancers of the colon, rectum, stomach, and endometrium in Dr Warthin's family G was later followed up by his colleagues, most recently by Henry Lynch, MD. Described today as a Lynch syndrome family, family G was last documented in 1971, prior to the modern era of molecular diagnostics.

OBJECTIVE

To update family G.

DESIGN, SETTING, AND PARTICIPANTS

Historical prospective cohort study of family G members from 1895 to 2000.

MAIN OUTCOME MEASURES

The primary outcomes were the frequencies and types of cancers, ages at diagnosis, and presence of the T to G transversion at the splice acceptor site of exon 4 of the mutS homolog 2, colon cancer, nonpolyposis type 1 (E coli) (MSH2) gene in family G members. A secondary analysis compared cancer-specific incidence rates in family G with published national and regional cancer incidence rates through the standardized incidence ratio (SIR).

RESULTS

Family G now has 929 known descendants of the original progenitor first reported in 1913. Cancers of the colon and rectum (SIR, 3.20; 95% confidence interval [CI], 2.39-4.19) and endometrium (SIR, 3.51; 95% CI, 1.92-5.89) continue to predominate in family G. Five of 40 tested members of family G carry the MSH2 T to G mutation; as a result, 15 of their living relatives are at increased risk of developing 1 or more colorectal or Lynch syndrome-associated cancers. In contrast, 97 living members of family G can now be excluded as mutation carriers.

CONCLUSION

Within the last decade, molecular diagnostic testing has transformed the care of family G and other Lynch syndrome families in which a pathogenic mutation has been identified.

A century of progress in hereditary nonpolyposis colorectal cancer (Lynch syndrome)

One of the earliest references to heredity in colorectal cancer dates to Aldred Warthin's now-famous recollection of his seamstress' distress regarding "cancer excess" in her family history. Her prediction of an early demise secondary to cancer of the female organs, colon, or stomach proved true. The slow, arduous investigation that ensued followed a tortuous route of nearly eight decades before the implications of such family histories were widely acknowledged through the designation of hereditary nonpolyposis colorectal cancer or Lynch Syndrome Variants I and II. The story of hereditary nonpolyposis colorectal cancer is one of chance meetings, the selfless sharing of information, perseverance in the face of adversity, meticulous scientific documentation, and ultimate vindication by a scientific process that yielded molecular genetic evidence through the identification of the culprit mutations (hMSH2, hMLH1, hPMS2, and hMSH6). Our purpose is to provide a brief outline of the course charted by the study of the genetics of hereditary nonpolyposis colorectal cancer. This should be of particular interest to the readers of this Journal as we celebrate 100 years of dedication to the diagnosis and treatment of diseases of the colon, rectum, and anus through the efforts of The American Society of Colon and Rectal Surgeons.

Diagnosis of hereditary non-polyposis colorectal cancer

The term hereditary non-polyposis colorectal cancer (HNPCC) was introduced initially to encompass autosomal dominant syndromes predisposing to colorectal cancer other than the polyposes. The term is a poor descriptor and is often applied to families on the basis of inadequate information. It is suggested that 'hereditary mismatch repair deficiency syndrome' (HMRDS) should replace the term HNPCC for describing the specific autosomal dominant condition which predisposes to cancer displaying the mutator phenotype. Population-based studies have shown that HMRDS probably accounts for no more than 2% of bowel cancer. A working diagnosis of HMRDS can be made on the basis of clinical, pathological and molecular characteristics. The histopathologist has an important role to play in the recognition and diagnosis of HMRDS. The characteristic morphology of colorectal cancer in HMRDS is reviewed and the diagnostic utility of 'field changes' and adenomas is discussed critically.

Molecular genetics and clinical-pathology features of hereditary nonpolyposis colorectal carcinoma (Lynch syndrome): historical journey from pedigree anecdote to molecular genetic confirmation

Hereditary nonpolyposis colorectal cancer (HNPCC), also termed Lynch syndrome, was originally called cancer family syndrome. Historically, in 1913 Aldred Warthin, a pathologist, published a family, now known as Family G, which had features of HNPCC. It was first delineated as a hereditary cancer syndrome in the mid-1960s by Lynch. There was an apparent autosomal dominant mode of inheritance of colorectal cancer and certain integral cancers, the most prominent of which was endometrial carcinoma. Prior to the discovery in 1993 and 1994 of genes (hMSH2, hMLH1, hPMS1, hPMS2) known as mis-match repair genes or mutator genes, the diagnosis of HNPCC rested exclusively upon evaluation of clinical findings in concert with a well-documented and extended pedigree. Thus, this disorder has evolved from a medical curiosity into a clinical syndrome wherein molecular biologists provided proof of its hereditary status. These discoveries should aid in elucidating its pathogenesis and carcinogenesis and in the next decade we likely will learn more about chemoprevention and surgical prophylaxis of HNPCC.

Hereditary nonpolyposis colorectal cancer: an update

Sporadic cancer develops approximately at 65 years of age. Epidemiologic data suggest that dietary factors probably are the most influential in colorectal carcinogenesis. In contrast, individuals who have relatives with colorectal neoplasia have an increased risk of these tumors themselves, which will appear earlier in life. The actual incidence of hereditary colorectal cancer is unknown. However, the incidence is much higher compared with well-known hereditary colorectal diseases, such as familial adenomatous polyposis.

OBJECTIVE

An overview of the recent progress in the field of both clinical and basic research on hereditary colorectal cancer must be made.

MATERIALS AND METHODS

Twenty-two family pedigrees were analyzed at Hamamatsu University School of Medicine, including the largest family pedigree in Japan, which contained 24 cases of colorectal cancer occurring over five generations. In 1995, when the International Symposium on Hereditary Cancer was held in Hamamatsu, 4,109 family pedigrees were investigated and analyzed, including 394 cases in 109 family pedigrees that met the Amsterdam Minimum Criteria. Information was collected by sending questionnaires to major hospitals in Japan. Basic updated data presented at the eighth and ninth International Collaborative Group on Hereditary Colorectal Cancer were also quoted.

RESULTS AND CONCLUSIONS

Because of the discovery of mismatch repair genes as that responsible for hereditary nonpolyposis colorectal cancer, modification of the Amsterdam Criteria is necessary. Replication error, as a mutator phenotype of mismatch repair genes, is a useful predictor of second primary malignancies. Surveillance or prophylactic surgery is still a controversial issue.

An update of HNPCC (Lynch syndrome)

Genetic epidemiology studies of colorectal cancer (CRC) can identify persons who are at inordinately high risk and who thereby might benefit from targeted early detection and primary prevention programs, inclusive of prophylactic surgery in selected cases. The discipline of molecular genetics has identified germline mutations that include APC in familial adenomatous polyposis (FAP) and mutator genes, namely MSH2, MLH1, PMS1, and PMS2 in hereditary nonpolyposis colorectal cancer (HNPCC). These discoveries have significantly enhanced our ability to identify individuals whose cancer destiny can literally be determined at birth. This review updates HNPCC's differential diagnosis, heterogeneity, tumor spectrum, newly found evidence of accelerated colonic adenoma to CRC, survival advantage, and currently available surveillance and management programs. Emphasis has been on how knowledge of the genetics and natural history of HNPCC can be used effectively to promote early diagnosis or prevention of cancer.

Clinical implications of advances in the molecular genetics of colorectal cancer

AIMS AND BACKGROUND

Hereditary nonpolyposis colorectal cancer (HNPCC) is the most common occurring hereditary form of colorectal cancer (CRC) where it accounts for as much as 10 percent of the total CRC burden. HNPCC is characterized by an autosomal dominant inherited predisposition to early age of onset (= 44 years) of CRC with proximal predominance (= 70% proximal to the splenic flecture) with an excess of synchronous and metachronous CRC (45% 10 years after initial hemicolectomy or segmental resection as opposed to subtotal colectomy), features which characterize the Lynch syndrome I variant, while the Lynch syndrome II variant of HNPCC shows all of these features, but in addition, there is a marked excess of carcinoma of the endometrium, ovary, small bowel, stomach, pancreas, and transitional cell carcinoma of the ureter and renal pelvis, lesions which are integral to this syndrome. Because of the early onset, we recommend colonoscopy to be initiated at age 25 and repeated every other year through age 35 and then annually thereafter. Women need to undergo endometrial aspiration biopsy at the time of initial colonoscopy.

METHODS AND RESULTS

Major advances in the molecular genetics of HNPCC have occurred during the past two years with identification of the hMSH2 gene at chromosome 2p and the hMLH1 gene at chromosome 3p, both of which have been cloned. PMS1 at chromosome 2p and PMS2 2 at chromosome 7q have also been implicated in HNPCC's etiology.

CONCLUSIONS

Genetic counseling is mandatory for presymptomatic DNA testing and for delivering information about the patient's germline status. Patients with germline mutations are offered prophylactic subtotal colectomy as an option to continued colonoscopy. It is now important for physicians to take careful cancer family histories so that this disorder can be readily identified, thereby enabling the initiation of highly targeted surveillance and management programs.

25 years of HNPCC

Research on the genetic, molecular genetic, clinical features, and natural history of HNPCC has shown tremendous progress and evolution during the past 25 years. Specifically, HNPCC's autosomal dominant mode of genetic transmission has now been documented through linkage studies of the gene at 2p (MSH2) and at 3p (MLH1) with the cloning of these genes. Also, the tumor spectrum has increased, which now, in addition to carcinoma of the colon, endometrium, stomach, and ovary, includes transitional cell carcinoma of the ureter and renal pelvis, and adenocarcinomas of the small bowel and pancreas. Surveillance and management protocols for patients at high risk should include full colonoscopy since 70% of the colon cancers occur in the proximal colon. Because of the marked excess of synchronous and metachronous colorectal cancers (CRC), no less than a subtotal colectomy should be performed at the time of initial CRC. Women, in addition to colonoscopy, require endometrial aspiration biopsy. Should they develop CRC and if their procreation is completed, we recommend that they consider prophylactic hysterectomy and bilateral salpingo oophorectomy at the time of their subtotal colectomy. Now that the deleterious genes at 2p and 3p have been identified, we are offering candidates, in whom the MSH2 or MLH1 mutation has been verified, an option of prophylactic subtotal colectomy as opposed to annual life time colonoscopy. With the development of the International Hereditary Nonpolyposis Colorectal Cancer Collaborative Group, knowledge can be disseminated worldwide about the public health importance of HNPCC and the need to implement highly targeted surveillance and management strategies in all clinical practice settings.

Genetic counseling and HNPCC

Cancer control objectives in HNPCC can be realized when patients who are at increased genetic risk receive intensive education about the natural history, as well as the surveillance and management recommendations that this diagnosis entails. It is only when family members are sufficiently informed about all of the pertinent clinical and genetic aspects of HNPCC that they can make the best possible decisions about those cancer control strategies which will likely impact heavily upon their lives. The sum total of these ramifications come under the rubric of genetic counseling. Our experience indicates that genetic counseling must embody all of the trust and confidence which is inherent in a physician/patient relationship. This involves the understanding that one is dealing with an ego-involved patient who may be very anxious and apprehensive about his or her cancer risk, as well as that of siblings and progeny. We have described the importance of psychodynamic factors which impact upon the genetic counseling process and often compel the counselor to assume the role of a psychotherapist.