This report demonstrated that in endometrial cancer, Lynch syndrome cannot be excluded even if MLH1 promoter hypermethylation is confirmed in cases with MLH1 and PMS2 protein loss detected using IHC.
Buchanan et al. proposed a strategy for screening for Lynch syndrome in endometrial cancer patients using MSI, IHC, and
MLH1 promoter methylation. They recommended performing IHC on tumor tissue samples from patients who develop endometrial cancer at or before 60 years of age [
7].
MLH1 germline mutation, epimutation [
14], or epigenetic silencing can be considered when MLH1 and PMS2 protein losses are detected. Buchanan et al. reported that mismatch repair IHC tumor testing had high sensitivity and poor positive predictive value [
7]. Therefore, it is necessary to conduct further examinations because of the poor positive predictive value.
BRAF testing in colon cancer is useful to rule out Lynch syndrome [
6]. However, the usefulness of
BRAF testing to detect endometrial cancer is unclear because
BRAF mutation is infrequently found [
15].
MLH1 promoter methylation testing is useful for distinguishing between
MLH1 germline mutation and epigenetic silencing. MLH1 promoter hypermethylation is far more responsible for losses of MLH1 and PMS2 protein using IHC than MLH1 germline mutation in the population based screening. Thus, cases with
MLH1 promoter hypermethylation in cancer tissue are generally classified as sporadic endometrial cancer with abnormal somatic mismatch repair gene [
7].
However, recently some reports showed cases with germline mutations among colorectal cancer cases in which although MLH1 and PMS2 proteins were lost by IHC,
MLH1 promoter hypermethylation was observed in cancer tissues [
11‐
13] (Table
1). These reports suggested that it is inappropriate to exclude Lynch syndrome based on a result of
MLH1 promoter hypermethylation. Hagen et al. reported that they confirmed
MSH2 germline mutation and somatic
MLH1 promoter hypermethylation in a 71-year-old female with confirmed MLH1, MSH2, MSH6, and PMS2 protein losses in the colon cancer tissues using IHC [
11]. Raymond et al. also reported confirmed
MSH6 germline mutation and somatic
MLH1 promoter hypermethylation in a 75-year-old female with losses of MLH1, MSH6, and MSH2 proteins in the colon cancer tissue samples using IHC and concluded that
MLH1 promoter hypermethylation does not exclude the diagnosis of Lynch syndrome [
12]. Rahner et al. examined
MLH1 promoter methylation from 60 carriers of
MLH1 germline mutation, 38 carriers of
MSH2 germline mutation, and 25 individuals without germline mutation.
MLH1 promoter methylation was observed in one carrier each of
MLH1 and
MSH2 germline mutations. Therefore, they concluded that
MLH1 promoter hypermethylation could not exclude the diagnosis of Lynch syndrome [
13]. In the National Comprehensive Cancer Network guidelines, when losses of MLH1 and PMS2 proteins are detected using IHC in the presence of somatic
BRAF mutations and
MLH1 promoter hypermethylation, it is recommended to consider genetic testing in cases of early onset and positive family history of Lynch-associated malignancies [
5]. In the present case, sporadic endometrial cancer was suspected based on the results of IHC and
MLH1 promoter methylation testing of endometrial cancer tissues.
MLH1 promoter methylation was not observed in the peripheral blood; however, a large deletion in exon 5 of this gene was observed. Therefore, we diagnosed the patient with Lynch syndrome. With respect to endometrial cancer, the coexistence of
MLH1 germline mutation and
MLH1 promoter hypermethylation in the same patient was absent in the range of our literature search. However, similar to colorectal cancer, when screening for Lynch syndrome using endometrial cancer tissue, this is a pitfall that should not be overlooked.
Table 1
Co-existed MLH1 hypermethylation and mismatch repair genes germline mutations
| CRC | – | – | – | – | N/A | Wild-type | + | MSH2 mutation |
| CRC | – | + | – | – | MSI-H | Wild-type | + | MSH6 mutation |
| CRC | – | + | + | – | MSI-H | N/A | + | MLH1 mutation |
Yokoyama et al. | EC | – | + | + | – | N/A | N/A | + | MLH1 mutation |
In summary, we have demonstrated that in endometrial cancer, similar to colorectal cancer, both MLH1 germline mutation and somatic MLH1 promoter hypermethylation may be observed in the same patient and that Lynch syndrome cannot be excluded even if MLH1 promoter hypermethylation is observed. From a cost perspective, it is considered prohibitive to conduct genetic testing for all cases that present with MLH1 promoter hypermethylation. However, it has been suggested that genetic testing should be considered in endometrial cancer patients with MLH1 promoter hypermethylation at least if clinical and family histories are indicative of Lynch syndrome.