Cancer risks in Lynch syndrome, Lynch-like syndrome, and familial colorectal cancer type X: a prospective cohort study

The study population was taken from a prospective registry study of the “German Consortium for Familial Intestinal Cancer” (formerly termed “German HNPCC Consortium”). Six university centres collected information about families suspected of having Lynch syndrome based on the Amsterdam-II criteria and/or revised Bethesda guidelines [15, 16]. All participants gave their written informed consent at registry inclusion, and the registry was approved by the Ethics Committees of all participating institutions.

A tissue sample (tumour or adenoma) of the index patient was examined for MMR deficiency (dMMR) using immunohistochemistry (IHC) and/or microsatellite analysis (MSA). In case of dMMR (or if no tissue sample was available), a germline mutation analysis of the MMR genes MLH1, MSH2, MSH6 and PMS2, and the EPCAM gene was carried out. Details about the diagnostic procedure are described elsewhere [17]. According to the results of the tissue and subsequent germline DNA analyses, index patients were classified as having LS (i.e. with a proven class 4/5 germline variant), LLS (i.e. fulfilling the Amsterdam-II and/or revised Bethesda criteria and not having a class 4/5 germline variant despite signs of dMMR in at least one family member), and FCCX (i.e. not having any signs of dMMR in the family while fulfilling the Amsterdam-II criteria). Relatives of LS index patients, who were predictively tested for the specific class 4/5 variant found in the index patient, were also considered as having LS if they were tested positive. Relatives of LLS and FCCX index patients were also considered as having LLS and FCCX, respectively. Individuals from families with dMMR due to MLH1 methylation were not regarded as having LLS.

Individuals with LS, LLS, or FCCX according to the above definitions were invited to participate in an intensified surveillance programme comprising annual colonoscopies, esophagogastroduodenoscopies, and gynaecological examinations. These individuals comprised both index patients and at-risk relatives. They were prospectively followed up and the result of each single surveillance examination was recorded in the registry.

Individuals were included in the present analysis if they had LS, LLS, or FCCX according to the above definitions. In the LS group, only MLH1, MSH2, and MSH6 carriers were included, whereas EPCAM and PMS2 carriers were excluded due to the low sample size. Additionally, all individuals had to have at least one colonoscopy after study registration and a prospective observation time of more than half a year.

From the above study population, eight different cohorts were defined and cancer risks were determined for the following eight types of cancers according to the International Classification of Diseases (ICD-10): any cancer (all Cxx without C77-C79), colorectal (C18-C20), stomach (C16), small bowel (C17), urothelial (C65-C68), female breast (C50), ovarian (C56), and endometrial cancer (C54.1). For each cancer type, its first incident occurrence was analysed. Individuals, who already had the cancer of interest before or within half a year after the start of prospective observation (prevalent cancers) were excluded. Therefore, patient numbers and observation times were different between the eight cohorts. Patients with prevalent cancers other than the cancer type of interest were not excluded. Females who had undergone a hysterectomy prior to the start of the prospective observation were excluded from the endometrial cancer and females with an oophorectomy from the ovarian cancer analyses.

Prospective observation started at the first colonoscopy after study registration or at age 25, whichever occurred last. Observation ended at the specific cancer event of interest, the age of 80, the last documented contact before May 12, 2019, or death, whichever came first. For calculations of endometrial cancer, hysterectomy was an additional reason for the end of observation, as well as oophorectomy for ovarian cancer. The incident occurrence of cancers other than the cancer type of interest was no reason for censoring [9, 10]. Cumulative cancer risks were determined for the different cancer types stratified by the three risk groups LS, LLS and FCCX, and by subgrouping the LS group into MLH1, MSH2 and MSH6 carriers. Risk estimation was done using the Kaplan-Meier product limit estimator accounting for the age at the beginning of prospective observation (left-truncation) [34]. For comparisons between groups, the log-rank test was used. The proportional hazards assumption was tested using scaled Schoenfeld residuals [35, 36]. In addition, the log-minus-log-transformed 95% confidence intervals of the product limit estimator were determined [34, 37]. In order to compare cancer risks with the general population, the standardised incidence ratio (SIR) was calculated, which is defined as the ratio between the observed number of cancers of interest and the expected number of cancers of interest in the general population. The number of expected cancers of interest was determined by the sum of all products of the age-specific incidence rates for the general population with the corresponding person-years. The source of age-specific incidence rates in 5-year-intervals for the general population in Germany (2000–2014) was the German Centre for Cancer Registry Data of the Robert Koch-Institute (Berlin, Germany. URL: www.​krebsdaten.​de/​abfrage). As information regarding skin malignancies except malignant melanoma was not available for the general population, individuals with such neoplasms were excluded from the SIR calculation of the cancer type “any cancer”. Ninety-five percent confidence intervals for SIRs were calculated assuming a Poisson distribution.

All reported testing was two-sided, and p-values lower than 0.05 were considered statistically significant. Statistical analyses were carried out with R 3.4.2 for Windows (R Core Team. R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URL: https://​www.​R-project.​org).

The study population comprised a total of 1830 patients, including 594 in the LLS, 116 in the FCCX group, and 1120 in the LS group (447 MLH1, 549 MSH2, and 124 MSH6 carriers). In total, 1200 individuals were index patients. The detailed patient characteristics for the eight different cancer types are summarised in Table 1 (a sex specific summary is shown in Additional file 1: Tables S1 and S2). The number of individuals at risk for first incident cancer ranged from 322 to 1102 in LS, 120 to 586 in LLS, and 40 to 116 in FCCX, depending on the cancer type. The median age at the start of the prospective observation ranged from 35 to 49 years depending on the risk group and cancer of interest. Table S3 in Additional file 1 shows a detailed summary of patient numbers, observation times and numbers of incident cancers. The types of cancers considered for the calculation of the type “any cancer” are given in Additional file 1: Table S4.

The risk for any cancer by the age of 70 years was 63.7% (95%CI 48.5–78.8%) for LS, 27.3% (95%CI 14.5–47.8%) for LLS, and 25.0% (95%CI 6.6–70.2%) for FCCX patients (Fig. 1 and Table 2). Cumulative cancer risk was higher for the LS group than for LLS or FCCX for any cancer, small bowel, urothelial, female breast, ovarian, and endometrial cancer. The risks in the FCCX group were lower than in the LLS group for all cancer types, except for female breast and ovarian cancer. The risk of any cancer, small bowel, urothelial, and endometrial cancer was statistically significantly higher in the LS group than in the LLS group. No statistically significant differences for “any cancer” were found in the sex-specific analyses, whereas significant differences were also observed in males for small bowel and urothelial cancer, but not in females. No incident colorectal cancer events were observed in the FCCX group. LLS patients showed a lower colorectal cancer risk (21.0%, 95%CI 9.9–41.3%) than LS patients (40.9%, 95%CI 28.3–56.4%) at age 70, but the difference between LS, LLS, and FCCX was not statistically significant (p = 0.102). There were no significant differences between the LLS and FCCX groups (Additional file 1: Figure S7).

Within the LS group, higher cancer risks were found for MLH1 and MSH2 carriers than for MSH6 carriers for any cancer, colorectal, stomach, small bowel, urothelial, and endometrial cancer (Fig. 2 and Table 2, Additional file 1: Figure S8). The risk of ovarian cancer was highest in MSH2 carriers (Additional file 1: Tables S5 and S6) with statistically significant differences between the three genes (p = 0.041). For urothelial cancer, risk differences were borderline non-significant (p = 0.055).

Moreover, we found significant differences in cancer risks between index patients and the at-risk relatives for colorectal and endometrial cancer in the LLS group. Index patients had a higher risk (p = 0.027) of colorectal cancer at age 70 (50.0%, 95%CI 19.6–88.9%) compared to their relatives (13.2%, 95%CI 4.4–35.9%), but a lower risk (p = 0.010) of endometrial cancer (4.0%, 95%CI 1.0–15.3% vs. 23.1%, 95%CI 8.1–55.8%).

Compared to the general population, cancer risks in the LS group were higher for all cancer types. These results were statistically significant for all cancer types regardless of sex, with the exception of female breast cancer (Fig. 3, Additional file 1: Figures S9 and S10). Standardised incidence ratios (SIRs) ranged from 5.3 for “any cancer” to 126.0 for small bowel cancer. Increased SIRs in MLH1 and MSH2 carriers were found in male LS patients for all types of cancer. These results were also statistically significant, except for stomach cancer where only MLH1 carriers had a significantly increased risk. The SIR of colorectal cancer was also elevated in male MSH6 carriers, although not showing statistical significance. Female MLH1 and MSH2 carriers had elevated SIRs for any cancer, colorectal, stomach, small bowel, urothelial, and endometrial cancer, which were all statistically significant, with the exception of stomach cancer in MLH1 carriers. In addition, female MSH2 carriers showed a significantly increased risk of ovarian cancer. The SIRs for female breast cancer were only slightly marginally elevated for MLH1 and MSH2 carriers compared to the general population, while the SIR for MSH6 carriers was statistically significantly higher.

Larger SIRs were observed in the LLS group for any cancer, colorectal, stomach, small bowel, urothelial, and endometrial cancer, which were statistically significant except for small bowel cancer. Regarding sex, significantly increased SIRs in the LLS group were detected in females for endometrial and urothelial cancer, as well as in males for colorectal and stomach cancer. Cancer risks were not statistically significantly increased in the FCCX group compared to the general population.