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    OpenPayerBilling CodesMalignant neoplasms of digestive organsICD-10-CM c21-malignant-neoplasm-of-anus-and-anal-canal
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    ICD-10-CM Code For Malignant Neoplasm Of Anus And Anal Canal: Group Overview

    The International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) code group C21 includes malignant neoplasms of the anus and anal canal, covering primary cancers of the anal verge, anal canal, and overlapping anorectal sites. These ICD-10-CM diagnosis codes are used to document clinical encounters for patients with primary malignant tumors in the distal anorectal region, capturing details such as tumor location and any specified extension. Accurate coding within the ICD-10-CM C21 group supports proper claim adjudication, complete clinical documentation, and appropriate reimbursement.

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    ICD-10-CM C21: Malignant Neoplasm Of Anus And Anal Canal Overview

    The International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) code group C21 covers malignant tumors originating in the anus and anal canal, representing cancers of the distal gastrointestinal tract. These diagnoses target the anorectal region and include primary malignancies of the anal verge, anal canal, and overlapping sites. Accurate coding is important for appropriate clinical documentation and impacts reimbursement, staging, and cancer registry reporting.

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    When to Use

    Use a code from this group when a diagnosis documents a primary malignant neoplasm of the anus or anal canal, including specified subsites or overlapping lesions. Select the most specific code available based on clinical documentation of tumor location and any extension or secondary involvement.

    ICD-10-CM Codes

    4 rows

    ICD-10-CM CodeDescription
    C21.0Malignant neoplasm of anus, unspecified
    C21.1Malignant neoplasm of anal canal
    C21.2Malignant neoplasm of cloacogenic zone
    C21.8Malignant neoplasm of overlapping sites of rectum, anus and anal canal

    DRG Codes

    3 rows

    DRG CodeDescription
    374Digestive Malignancy with MCC
    375Digestive Malignancy with CC
    376Digestive Malignancy without CC/MCC

    Typical Clinical Scenarios

    • An adult patient presents to the emergency department with acute rectal bleeding and severe anal pain after noticing a rapidly enlarging, ulcerated mass at the anal verge. Physical exam and anoscopy reveal a friable lesion confined to the anal margin without obvious extension into the canal; biopsy is performed confirming invasive squamous cell carcinoma of the anal margin. A diagnosis from this group is assigned because the neoplasm arises at the anal margin requiring staging and urgent oncology/surgical evaluation. Typical codes: C21.0, C21.8
    • A middle-aged patient in outpatient colorectal surgery clinic with several months of intermittent rectal bleeding, tenesmus, and a palpable lesion within the anal canal on digital exam; biopsy shows invasive carcinoma of the anal canal. This chronic, progressive presentation leads to diagnostic workup, imaging for local extent and nodal involvement, and treatment planning for chemoradiation or surgery, prompting assignment of the anal canal malignancy code. Typical codes: C21.1, C21.8
    • A patient with known colorectal malignancy under surveillance is found on follow-up imaging and anoscopic exam to have a metastatic lesion involving both the anal canal and the perianal skin with multiple nodules and ulceration, complicating wound care and causing persistent drainage. Because the malignant process now involves contiguous anal structures and perianal tissues requiring palliative interventions and symptom management, a specific code from this group reflecting involvement of both sites is assigned. Typical codes: C21.2, C21.8

    Related Codes

    C15-MALIGNANT-NEOPLASM-OF-ESOPHAGUS

    ICD-10-CM Code For Malignant Neoplasm Of Esophagus: Group Overview

    C16-MALIGNANT-NEOPLASM-OF-STOMACH

    ICD-10-CM Code For Malignant Neoplasm Of Stomach: Group Overview

    C17-MALIGNANT-NEOPLASM-OF-SMALL-INTESTINE

    ICD-10-CM Code For Malignant Neoplasm Of Small Intestine: Group Overview

    C18-MALIGNANT-NEOPLASM-OF-COLON

    ICD-10-CM Code For Malignant Neoplasm Of Colon: Group Overview

    C19-MALIGNANT-NEOPLASM-OF-RECTOSIGMOID-JUNCTION

    ICD-10-CM Code For Malignant Neoplasm Of Rectosigmoid Junction: Group Overview

    C20-MALIGNANT-NEOPLASM-OF-RECTUM

    ICD-10-CM Code For Malignant Neoplasm Of Rectum: Group Overview

    C22-MALIGNANT-NEOPLASM-OF-LIVER

    ICD-10-CM Code For Malignant Neoplasm Of Liver And Intrahepatic Bile Ducts: Group Overview

    C23-MALIGNANT-NEOPLASM-OF-GALLBLADDER

    ICD-10-CM Code For Malignant Neoplasm Of Gallbladder: Group Overview

    C24-MALIGNANT-NEOPLASM-BILIARY-TRACT

    ICD-10-CM Code For Malignant Neoplasm Of Other And Unspecified Parts Of Biliary Tract: Group Overview

    C26-MALIGNANT-NEOPLASM-OTHER-ILL-DEFINED-DIGESTIVE-ORGANS

    ICD-10-CM Code For Malignant Neoplasm Of Other And Ill-Defined Digestive Organs: Group Overview

    Frequently Asked Questions

    References

    1. 1.CPT® Codes and Descriptions. AAPC. Retrieved Aug 11, 2026.Maintains the CPT code set's official descriptions and guidelines, licensed from the American Medical Association, used as the definitional source for CPT codes on this page.
    2. 2.HCPCS Quarterly Update. Centers for Medicare & Medicaid Services (CMS). Retrieved Aug 11, 2026.CMS's quarterly release of HCPCS Level II codes and short/long descriptors, the source for HCPCS code definitions and update history.
    3. 3.ICD-10-CM Full Code List. Centers for Medicare & Medicaid Services (CMS). Retrieved Aug 11, 2026.CMS's complete ICD-10-CM diagnosis code list, used to cross-reference diagnosis codes associated with this procedure or service.
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