Summary & Overview
HCPCS M1194: Documentation of Absent or Deferred MMR/MSI Testing
Headline: HCPCS Level II code M1194 flags absent or deferred MMR/MSI testing documentation in surgical pathology reports
Lead: HCPCS Level II code M1194 captures documentation that surgical pathology reports did not include an impression, conclusion, or recommendation for mismatch repair (MMR) testing by immunohistochemistry or microsatellite instability (MSI) testing by DNA-based methods, or that those tests were not performed due to clinical or specimen limitations.
What this code represents and why it matters: The code identifies cases where tumor profiling for MMR/MSI — assays that can inform immunotherapy decisions such as checkpoint inhibitor use — is not documented or not feasible. Nationally, consistent documentation of these testing decisions affects clinical decision-making, care coordination between surgical pathology and oncology, and downstream quality measurement.
Key payers covered: Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare.
Overview of what readers will learn: This publication explains the clinical context and service setting for M1194, typical scenarios leading to its use (e.g., tissue exhaustion, neoadjuvant therapy, limited tumor), and the implications for pathology and oncology workflows. Readers will find benchmarks and payer coverage patterns where available, a summary of relevant modifiers and documentation practices, and discussion of how M1194 fits into quality reporting and care pathways. Data not available in the input are noted where specific payer policies, taxonomies, ICD-10 mappings, and related codes would otherwise be detailed.
Billing Code Overview
HCPCS Level II code M1194 documents when surgical pathology reports lack an impression, conclusion, or recommendation for testing of MMR by immunohistochemistry, MSI by DNA-based testing, or when both tests were not included. The description covers scenarios such as when the patient will not be treated with checkpoint inhibitor therapy, no residual carcinoma is present in the sample (tissue exhausted or status post neoadjuvant treatment), or there is insufficient tumor for testing.
Service type: Pathology documentation of absent or deferred mismatch repair (MMR) and microsatellite instability (MSI) testing.
Typical site of service: Hospital pathology laboratory, surgical pathology service, or outpatient pathology laboratory associated with surgical specimen processing.
Clinical & Coding Specifications
Clinical Context
A 62-year-old patient undergoes surgical resection of a colorectal tumor. The surgical pathology report documents histologic findings but does not include an impression, recommendation, or testing status for mismatch repair by immunohistochemistry (MMR IHC) or microsatellite instability by DNA-based testing (MSI by DNA). The pathology team documents the medical reasons testing or an impression could not be provided: the specimen is exhausted after diagnostic sections and ancillary studies, neoadjuvant therapy resulted in no residual carcinoma, or insufficient tumor cellularity for valid testing. The specimen and report are reviewed at multidisciplinary tumor board; medical oncology notes that checkpoint inhibitor therapy is not currently indicated given lack of actionable testing or alternative treatment plan. The laboratory codes the case with HCPCS Level II code M1194 to document the medical reason testing or an impression for MMR/MSI was not included. Typical workflow steps include specimen accessioning, histologic evaluation, attempt to block tissue for IHC or molecular assays, documentation of insufficient tissue or clinical rationale for omitting testing, communication of results to the treating clinician, and tumor board discussion when applicable. Typical site of service is hospital-based surgical pathology or independent pathology laboratory associated with inpatient or outpatient surgical procedures. Typical patient scenarios include post-resection colorectal carcinoma after neoadjuvant therapy, small biopsy specimens with exhausted tissue, or clinical situations where checkpoint inhibitor therapy is not planned and testing was deferred for clinical reasons.
Coding Specifications
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