Table 1.
Patient and tumor characteristics.
| Characteristics (n = 99) | n (%) |
|---|---|
| Median age (years, range) | 59.0 [17, 98] |
| Gender (n = 99) | |
| Female | 47 (47.5%) |
| Male | 52 (52.5%) |
| TNM stage at diagnosis (n = 99) | |
| I–II | 14 (14.2%) |
| III | 31 (31.3%) |
| IV | 54 (54.5%) |
| Primary tumour site (n = 98 *) | |
| Right colon | 65 (66.3%) |
| Left colon | 28 (28.6%) |
| Rectum | 5 (5.1%) |
| Grade (n = 98 *) | |
| Poorly differentiated | 38 (39.6%) |
| Moderately differentiated | 43 (44.8%) |
| Well differentiated | 15 (15.6%) |
| Missing | 2 |
| RAS status on primary tumors (n = 98 *) | |
| Mutated | 20 (23.3%) |
| Wild-type | 66 (76.7%) |
| Missing | 12 |
| BRAFV600E status on primary tumors (n = 98 *) | |
| Mutated | 36 (38.3%) |
| Wild-type | 58 (61.7%) |
| Missing | 4 |
| MLH1 promoter hypermethylation (n = 75 **) | |
| Yes | 46 (70.8%) |
| No | 19 (29.2%) |
| Missing | 10 |
| Lynch syndrome or sporadic cases (n = 99) | |
| Proven Lynch syndrome (MMR gene mutation) | 20 (20.8%) |
| Suspected Lynch syndrome | 21 (21.9%) |
| Sporadic case | 55 (57.3%) |
| Missing | 3 |
* One patient has no primary tumor sample available. ** Only tumors with MLH1 and/or PMS2 loss were tested for MLH1 promoter hypermethylation. TNM: tumor, node, metastasis; MMR: mismatch repair; IHC: immunohistochemistry. Most primary tumors were right-sided (66.3%), poorly or moderately differentiated (84.4%) and stage III or IV at diagnosis (85.8%). All primary tumors were dMMR and had MSI status with no discordance. Most tests were performed before any treatment (92.9%). Among primary tumors, most presented a loss of MLH1 and PMS2 (70.4%) or a loss of MSH2 and MSH6 (17.3%) detected by MMR IHC (Table 2). RAS and BRAFV600E mutations were observed in 23.3% and 38.3%, respectively. All in all, 57.3% were sporadic cases, 42.7% were suspected or proven LS.