Study design and patient population

The study design was approved by the institutional review board of Hamamatsu University School of Medicine (IRB number:16–138). We prospectively collected the records of 566 patients who underwent colorectal surgery between September 2016 and November 2021 at Hamamatsu University School of Medicine. Among them, 24 patients who underwent endoscopic resection at the other hospitals and 20 patients who did not give consent to participate in this study were excluded. Finally, 522 patients were included.

Immunohistochemistry for MMR proteins

In September 2016, we started to perform universal screening using immunohistochemistry (IHC) for four MMR proteins (MLH1, MSH2, MSH6, and PMS2) according to the manufacturer’s protocol, in 4-µm-thick formalin-fixed paraffin-embedded sections. MMR proteins (MMRP) was evaluated using endoscopically resected specimens or surgically resected specimens.

The primary antibodies used for detecting the MMRP were anti-hMLH1 antibody (clone G168-728; BD Biosciences; 1:100), anti-hMSH2 antibody (clone FE11; Calbiochem; 1:100), anti-MSH6 antibody (clone 44/MSH6; BD Biosciences; 1:100), and anti-hPMS2 antibody (clone A16-4; BD Biosciences; 1: 100) until June 2021. From July 2021, fully automated IHC and in situ hybridization slide-staining system began to be used. Accordingly, the VENTANA detection kits were used for evaluation, anti-MLH1 antibody (clone M1; Roche), anti-MSH2 antibody (clone G219-1129; Roche), anti-MSH6 antibody (clone SP93; Roche), and anti-PMS2 antibody (clone A16-4; Roche).

The normal staining patterns for MLH1, MSH2, MSH6, and PMS2 are unclear. However, the absence of nuclear staining in the tumor cells in the presence of nuclear staining of non-neoplastic cells, such as normal colonic epithelial cells, lymphocytes, or stromal cells, was considered to represent an abnormal pattern. This evaluation method is performed in accordance with the Japanese Society for Cancer of the Colon and Rectum Guidelines 2016 and 2020 for the Clinical Practice of Hereditary Colorectal Cancer [12, 13]. The staining results were evaluated by consensus between two independent pathologists. Tumors with loss of expression of either protein were designated as deficient MMR (dMMR).

Pre-multistep approach with multidisciplinary team (P-MA)

Before a multistep screening with multidisciplinary team, the surgeons explained the possibility of LS to all patients diagnosed with dMMR. Only those who make a request received genetic counseling by medical geneticists (Fig. 1). On the other hand, we interviewed all patients who did not receive genetic counseling to know why they refused it.

Fig. 1

Flow charts of the universal screening for Lynch syndrome over time

In the pre-multidisciplinary team management group, only surgeons explained the possibility of LS and referred patients to receive genetic counseling. In the multidisciplinary team management group, surgeons, genetic counselors, and medical geneticists each have their own role

dMMR: deficient MMR, LS: Lynch syndrome, CRC: colorectal cancer

Multistep approach with multidisciplinary team (MA)

Based on the result of the interviews, we started a multidisciplinary team in January 2020. A multidisciplinary team consists of six surgeons, one genetic counselor, one medical geneticist, and six pathologists.

Figure 1 showed the comparison of a medical practice flow chart for dMMR patients before and after MA. As the first step, the pathologist and surgeon confirmed the pattern of protein expression loss. When a tumor showed loss of MLH1 and PMS2 expression, the surgeons determined whether the following exclusion criteria were applied or not. Exclusion criteria were first-episode CRC, 70 years old and above at CRC diagnosis, and no family history of cancer. For the remaining cases, the surgeons refer the patient for hereditary CRC and recommend that the patients undergo pre-genetic counseling with a genetic counselor on the same day or within a week. In the case of a protein expression loss pattern other than MLH1 and PMS2, the surgeons refer the patient for hereditary CRC and recommend that the patients undergo pre-genetic counseling with a genetic counselor as well. As the second step, the genetic counselor performed free-of-charge pre-genetic counseling by reviewing the family history for cancer, outlining the genetic disease, listening to the patient’s concerns, and explaining the flow of medical examination. Then, genetic counseling was offered to patients who requested specialist medical examination following pre-genetic counseling. After genetic counseling by medical geneticists and genetic counselor, patients underwent genetic testing, which was performed on peripheral blood samples.

Assessment of MA performance

In this study, patients were divided into the following two groups: P-MA group for patients before multistep approach with multidisciplinary team and MA group for those after multistep approach with multidisciplinary team. We evaluated the changes in the rates of genetic counseling and genetic testing as well as the diagnostic rate of LS-associated CRC between P-MA and MA groups.

Statistical analysis

Statistical analyses were conducted using JMP® 16 (SAS Institute Inc., Cary, NC, USA). Continuous variables were expressed by median and range and tested using the Mann–Whitney U test. Categorical data were analyzed using Fisher’s exact test or the Chi-squared test as appropriate. Bonferroni corrections were applied to correct for multiple tests. P-values < 0.05 were considered as statistically significant.