Download possible relevant diagnosis codes for MSI-H/dMMR CRC

The following codes as of July 2021 are provided as a reference and may be relevant when billing for KEYTRUDA and its administration. Consult the relevant manual and/or other guidelines for a description of each code to determine the appropriateness of its use and for information on additional codes. Diagnosis codes should be selected only by a health care professional. You are solely responsible for determining the appropriate codes and for any action you take in billing.

When submitting a claim for KEYTRUDA, always verify coding requirements with the relevant payer. Coding requirements may vary by insurer or plan; please refer to the payer-specific policies to understand what may be covered.

Check with the relevant payer regarding guidance on which diagnoses they will recognize and the applicability of secondary codes. Health care professionals are solely responsible for selecting codes that appropriately reflect the patient’s diagnosis, the services rendered, and the applicable payers’ guidelines.

Providers should document the diagnosis with a sufficiently high degree of specificity based on the information available to enable the identification of the most appropriate code. Although CMS has said that an unspecified code may be appropriate in some cases, CMS has advised that you should always code with as much specificity as possible consistent with the clinical documentation.

Merck and its agents make no warranties concerning the accuracy or appropriateness of this information for your particular use given the frequent changes in public and private payer billing. Merck cautions that payer-coding requirements vary and can frequently change, so it is important to regularly check with each payer or, where applicable, the Medicare Administrative Contractor as to payer-specific requirements. The use of this information does not guarantee payment or that any payment received will cover your costs.


KEYTRUDA is indicated for the treatment of patients with unresectable or metastatic microsatellite instability-high (MSI-H) or mismatch repair deficient (dMMR) colorectal cancer (CRC).

FDA-Approved Dosing

The FDA-approved dose of KEYTRUDA is either 200 mg administered as an intravenous infusion over 30 minutes every 3 weeks or 400 mg administered as an intravenous infusion over 30 minutes every 6 weeks, until disease progression, unacceptable toxicity, or up to 24 months.

This indication is approved under accelerated approval based on pharmacokinetic data, the relationship of exposure to efficacy, and the relationship of exposure to safety. Continued approval for this dosing may be contingent upon verification and description of clinical benefit in the confirmatory trials.

Possible relevant diagnosis codes for advanced MSI-H/dMMR CRC

Learn more about each diagnosis code and descriptor by selecting from the series options below.

When assigning ICD-10-CM for MSI-H/dMMR advanced tumors treated with KEYTRUDA, identify the appropriate ICD-10-CM category for the advanced malignant neoplasm of the body part under treatment and select the code based on the specific site. For example: C18.6 malignant neoplasm of descending colon.


C18: Malignant Neoplasm of Colon5

The C18 series excludes malignant carcinoid tumors of the colon; C18.7 excludes malignant neoplasm of rectosigmoid junction

C18.0 Malignant neoplasm of cecum
C18.1 Malignant neoplasm of appendix
C18.2 Malignant neoplasm of ascending colon
C18.3 Malignant neoplasm of hepatic flexure
C18.4 Malignant neoplasm of transverse colon
C18.5 Malignant neoplasm of splenic flexure
C18.6 Malignant neoplasm of descending colon
C18.7 Malignant neoplasm of sigmoid colon
C18.8 Malignant neoplasm of overlapping sites of colon
C18.9 Malignant neoplasm of colon, unspecified

C19: Malignant Neoplasm of Rectosigmoid Junction5

The C19 series excludes malignant carcinoid tumors of the colon

C19 Malignant neoplasm of rectosigmoid junction

C20: Malignant Neoplasm of Rectum5

The C20 series excludes malignant carcinoid tumor of the rectum

C20 Malignant neoplasm of rectum

C21: Malignant Neoplasm of Anus and Anal Canal5

The C21 series:

  • Excludes: malignant carcinoid tumors of the colon, malignant melanoma of anal margin, malignant melanoma of anal skin, malignant melanoma of perianal skin, other and unspecified malignant neoplasm of anal margin, other and unspecified malignant neoplasm of anal skin, other and unspecified malignant neoplasm of perianal skin
C21.8 Malignant neoplasm of overlapping sites of rectum, anus and anal canal