Summary & Overview

HCPCS M1193: Surgical Pathology Report for MMR/MSI Testing

HCPCS Level II code M1193 denotes surgical pathology reports that include an impression or conclusion about mismatch repair (MMR) status by immunohistochemistry, microsatellite instability (MSI) status by DNA-based testing, or a recommendation to perform those tests. This code is important nationally as MMR and MSI testing guide cancer diagnosis, prognostication, and therapy selection, including immunotherapy decisions and hereditary cancer evaluations. Payers commonly engaged in coverage and reimbursement for these pathology services include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare.

Readers will find a concise overview of the clinical context for reporting MMR and MSI results, typical service settings, and which payers are relevant for coverage considerations. The publication summarizes coding use and documentation expectations for surgical pathology reports, presents payer coverage scope, and highlights how MMR/MSI status is positioned within diagnostic workflows and downstream care decisions. Data not available in the input will be identified as such where relevant.

AetnaBlue Cross Blue ShieldCigna HealthUnitedHealthcareMedicareM1193HCPCS Level IIsurgical pathologyMMR testingMSI testingmolecular diagnosticsoncology pathologypathology reportingdiagnostic testing

Billing Code Overview

HCPCS Level II code M1193 describes surgical pathology reports that contain an impression or conclusion of, or a recommendation for testing of, MMR by immunohistochemistry, MSI by DNA-based testing status, or both. This code applies to pathology documentation that communicates results or advises molecular testing for mismatch repair (MMR) protein expression via immunohistochemistry and/or microsatellite instability (MSI) status determined by DNA-based methods.

Service type: Pathology consultation and diagnostic reporting that interprets tumor testing for MMR and/or MSI status
Typical site of service: Hospital pathology laboratories, independent pathology labs, and outpatient surgical pathology services

Clinical & Coding Specifications

Clinical Context

A 62-year-old patient undergoes surgical resection of a colorectal mass. The surgical pathology specimen is processed and the final pathology report includes a diagnostic impression recommending or reporting testing for mismatch repair (MMR) protein expression by immunohistochemistry (IHC) and/or microsatellite instability (MSI) status by DNA-based testing. This service typically occurs after grossing, histologic review, and pathologist interpretation of hematoxylin and eosin slides when features suggest possible Lynch syndrome, sporadic MMR deficiency, or when tumor features (e.g., high-grade histology, tumor-infiltrating lymphocytes, mucinous features) prompt reflex biomarker testing.

Workflow steps:

Specimen accessioning and gross description by pathology staff.
Tissue processing, embedding, sectioning, and H&E slide review by pathologist.
Pathologist documents impression recommending or ordering MMR testing by IHC, MSI testing by DNA-based methods, or both in the surgical pathology report.
If performed, laboratory runs IHC for MLH1, MSH2, MSH6, PMS2 and/or PCR/NGS-based MSI panel; results are incorporated into the final report or issued as an addendum.
Final report containing the impression and MMR/MSI test results is released to the surgical team and the ordering clinician for treatment planning and genetic counseling as indicated.

Typical site of service: hospital outpatient pathology/laboratory, hospital inpatient pathology, independent reference laboratory, or integrated academic pathology department.

Typical patient scenario: adult with colorectal carcinoma, endometrial carcinoma, or other tumors where MMR deficiency impacts prognosis, immunotherapy eligibility, and hereditary cancer evaluation.

Coding Specifications

Modifier	Description	When to Use
`22`	Increased procedural services	Use when documentation supports substantially greater work or complexity for the pathology service beyond typical for report generation and interpretation related to MMR/MSI testing recommendations.
`23`	Unusual anesthesia	Not typically used for this pathology coding; included only if applicable to a concurrent operative service.
`52`	Reduced services	Use when MMR/MSI testing or report elements were partially reduced or not fully performed.
`53`	Discontinued procedure	Use if intraoperative findings led to termination of a related operative procedure; rarely appended to pathology billing.
`54`	Surgical care only	Use on operative procedure claims when the surgeon provides only surgical component; not typically appended to pathology report code but may be present on related surgical claims.
`55`	Postoperative management only	Use on surgical claims where only postoperative care was provided; not typically for pathology billing.
`56`	Preoperative management only	Use on related preoperative evaluation claims; rarely used with pathology codes.
`62`	Two surgeons	Use on related surgical claims when two surgeons are involved; not typically appended to pathology service code.
`AS`	Ambulatory surgical center	Use on related facility claims to indicate ASC site of service when specimen originated from an ASC procedure.
`CO`	Catastrophe/disaster emergency	Use to indicate care during declared disaster/emergency when applicable to associated services.
`CQ`	Service furnished by an assistant at independent clinics	Use when an assistant provides portions of the service in qualifying settings; rarely used on pathology codes.
`FX`	Primary surgeon	Use on related surgical claims to identify the primary surgeon; not typically used on pathology coding.
`FY`	Assistant surgeon	Use on related surgical claims when an assistant surgeon performed the service; not typically used on pathology claims.
`QK`	Medical direction of two-physician assistant(s)/NPPs	Use on anesthesia or supervision claims where applicable; not typical for pathology billing.
`QX`	Service furnished by assistant physician	Use where an assistant physician provides services; not typical for pathology code billing.

Taxonomy Code	Specialty	Notes
`207P00000X`	Anatomic Pathology	Pathologists interpreting surgical specimens and ordering MMR/IHC or MSI testing.
`208000000X`	Pathology	General pathology services within hospital or reference lab settings.
`207L00000X`	Hematopathology	Hematopathologists may be involved when hematologic malignancies require MMR/MSI evaluation.
`207K00000X`	Anatomic and Clinical Pathology	Combined practice providing diagnostic interpretation and coordinating molecular testing for MSI.
`207RC0000X`	Molecular Genetic Pathology	Specialists who interpret DNA-based MSI testing and correlate with IHC results.

ICD-10 Code	Description	Clinical Relevance
`C18.9`	Malignant neoplasm of colon, unspecified	Colorectal cancers commonly prompt MMR IHC and MSI testing to evaluate for Lynch syndrome and immunotherapy eligibility.
`C54.1`	Malignant neoplasm of endometrium	Endometrial carcinomas are frequently screened for MMR deficiency and MSI to guide prognosis and genetic evaluation.
`C56.9`	Malignant neoplasm of ovary, unspecified	Certain ovarian tumors may undergo MMR/MSI testing when clinical or histologic features suggest MMR deficiency.
`D57.0`	Sickle-cell anemia with crisis	Example comorbidity where pathology services are performed for tissue specimens; not a primary indication for MMR/MSI testing but included in broader medical context.
`Z80.0`	Family history of primary malignant neoplasm of digestive organs	Family history may prompt reflex MMR/MSI testing and genetic workup when present in the surgical pathology context.

CPT Code	Description	Relationship to This Procedure
`88305`	Level IV surgical pathology, gross and microscopic examination	Common primary code for microscopic examination and diagnostic pathology report that may include recommendation for MMR/MSI testing; billed for the anatomic pathology interpretation.
`88342`	Immunohistochemistry, per specimen; initial single antibody stain	Used when performing IHC for individual MMR proteins (eg, MLH1, MSH2, MSH6, PMS2); multiple units billed for each antibody.
`88360`	Morphometric analysis, immunohistochemistry or immunocytochemistry, quantitative	Occasionally used when image analysis or quantification of IHC staining is reported for MMR markers.
`81275`	MSI (microsatellite instability) testing, examples by PCR/fragment analysis or NGS (varies by platform)	Represents DNA-based MSI testing; used when MSI status is determined by molecular methods and reported alongside the surgical pathology impression.
`88361`	Special stains (each beyond routine), for example, histochemical stains	May be used for additional special stains that support the diagnostic impression leading to MMR/MSI testing.
`88399`	Unlisted pathology procedure	Used when a novel or combined molecular pathology service related to MMR/MSI does not have a specific CPT and requires an unlisted code with supporting documentation.

OpenPayer