Hereditary Cancer and Genetic Testing

Cancer treatment for people with MLH1 mutations

Experts are conducting research studies to learn which treatments work best for people with an inherited MLH1 mutation. To learn more about standard of care treatment options for specific types of cancer, visit our section on Cancer Treatment by Cancer Type

Most cancers in people with an inherited MLH1 mutation will have a tumor biomarker known as MSI-high" or "MSI-H" (microsatellite instability). This biomarker indicates that the tumor has a feature known as "mismatch repair deficiency," which is also known by the abbreviations dMMR or MMR-D. Testing tumors for mismatch repair deficiency or MSI-High can be important, because these tumors are more likely to respond to immunotherapy agents known as immune checkpoint inhibitors

People with an MLH1 mutation may qualify for clinical trials looking for more effective treatments for cancer.

MSI-H colorectal cancer

  • In people with stage 2 colorectal cancer, MSI-high cancers have a good prognosis and may not benefit from 5-flourouracil (chemotherapy used in colorectal cancer) adjuvant therapy. 
  • Keytruda (pembrolizumab) is an immune checkpoint inhibitor used to treat metastatic or advanced colorectal cancer that has progressed following treatment with a fluoropyrimidine, oxaliplatin, and irinotecan.
  • Opdivo (nivolumab) is an immune checkpoint inhibitor used alone or in combination with Yervoy (ipilimumab) for metastatic cancer that has progressed following treatment with a fluoropyrimidine, oxaliplatin, and irinotecan.

Immune checkpoint inhibitors for treating any MSI-H cancer

  • Keytruda (pembrolizumab) is approved for the treatment of any solid tumors that test MSI-H, have progressed after treatment and for which there are no other treatment options.


dMMR endometrial cancer

  • Jemperli (dostarlimab) is an immunotherapy that is approved to treat recurrent and advanced endometrial cancer that is mismatch repair-deficient.

If you have an MLH1 mutation and have been diagnosed with cancer, you can find peer support through the following resources:


The majority of public and private health insurance plans are required to cover cancer diagnosis and treatment; copays, coinsurance and deductibles often apply. Patient costs and coverage for specific doctors, facilities or treatments may vary based on your health plan. If your insurance company denies your claim, your health care provider can help you write an appeal letter, or you can use one of our sample appeal letters. Visit our section on Insurance and Paying for Care: Treatment for more information.


The following cancer treatment studies may be of interest to people with an inherited MLH1 mutation. 

Advanced solid tumors of any type 

Colorectal cancer

Endometrial cancer

Prostate cancer

  • NCT04019964: Nivolumab in Biochemically Recurrent dMMR Prostate Cancer. Men who previously received definitive treatment for prostate cancer and later develop detectable prostate specific antigen (PSA) levels, have biochemically recurrent prostate cancer. A non-hormonal therapy such as nivolumab would provide an alternative to ADT in patients with biomarker selected (i.e. dMMR, MSI-H, high TMB, or CDK12-altered) biochemically recurrent prostate cancer.

Visit our Research Search and Enroll Tool to find additional studies.  

Last updated September 04, 2021