C20 ICD-10-CM Code: Malignant neoplasm of rectum

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for C20 in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2027Effective: October 1, 2026

Notes without a marker are published on C20 itself; “inherited from” names the category or block whose note applies here.

Coder workflow for C20

MedCoder structured workflow — derived from this code’s own official record

Before you code C20

1. Confirm the documented site and behavior (this code’s block classifies malignant neoplasms), whether the site is primary or secondary, and whether the malignancy is current or a personal history: a previously excised malignancy with no further treatment and no evidence of disease is history, not current disease. Verify the site against the Table of Neoplasms. Neoplasm chapter guidelines (Guidelines I.C.2.a, I.C.2.d, I.C.2.m).

   See the Table of Neoplasms entries · Guide: Active cancer vs history of cancer →

2. Check the Excludes1 note: if the documentation supports a condition named there, do not simply proceed with C20. Excludes1 conditions are not reported together with this code unless the record shows they are unrelated (Guidelines I.A.12.a).

   See the official tabular notes

Choose the right path

1. Does the documentation support a condition named in C20’s Excludes1 note?
   Yes → Do not simply proceed: review the excluded code. Both are reported only when the record shows the two conditions are unrelated.
   No → Continue.

   ReviewC7A.026, C46.4

Consider C20. Then confirm the code is valid for the date of service in the Verify section.

Documentation check

The provider’s diagnostic statement

Codes are assigned from the provider’s documented diagnosis, not from clinical criteria, test values or a medication list (Guidelines I.A.19).

Anatomical site

At the most specific level the record states; a site the classification separates cannot be assumed from a procedure or a measurement.

Behavior and current-versus-history status

Malignant, in situ, benign or uncertain; primary or secondary; current disease or personal history (Guidelines I.C.2.m).

Official instructions as workflow

• Excludes1 — check before selecting C20(2 notes)

  Coding workflow: If the documentation supports a condition named in this note, do not simply proceed with C20: the two are not reported together. The one exception is when the record shows the two conditions are unrelated to each other.

  CompareC7A.026, C46.4

  See the official tabular notes · Guidelines I.A.12.a

• Excludes2 — not part of C20(1 note)

  Coding workflow: The conditions named in this note are not included in C20. When the record documents both, both may be reported; the note is a boundary, not a prohibition.

  CompareC49.A

  See the official tabular notes · Guidelines I.A.12.b

Coding decision scenarios

Pattern scenarios for this code’s structure — decision rules, not clinical cases

Every row is derived from this code’s own record — its title, tabular notes, 7th-character family and same-category siblings — with fixed MedCoder wording; nothing is inferred about a patient. The official notes and guideline text are in the sections each row links to, and they control.

Neoplasm Table Sites (1)

Official source data — entries quoted as published, in the Index’s own lookup phrasing

Anatomical sites from the official ICD-10-CM Table of Neoplasms that map to this code, with the matching behavior column.

• Neoplasm, neoplastic, rectum (ampulla) — Malignant, Primary

Don’t confuse C20 with…

MedCoder analysis — pairs from this code’s official notes, distinctions written by MedCoder

The codes most likely to be picked instead of C20 — named in its own official notes, or sharing its laterality or encounter family — with what separates them and which documentation moves the case. Each links to the full comparison.

• C7A.026— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of malignant carcinoid tumor of the rectum moves the case to C7A.026; the two are not reported together unless documented as unrelated.

  Full comparison: C20 vs C7A.026 →

• C46.4— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of Kaposi's sarcoma of gastrointestinal sites moves the case to C46.4; the two are not reported together unless documented as unrelated.

  Full comparison: C20 vs C46.4 →

• C49.A— Excludes2 relationship (Informational)

  Distinct conditions — both may be reported.

  A distinct condition — both may be reported when both are documented.

  What moves you there: Documentation of gastrointestinal stromal tumors adds C49.A; it is not part of this code and both may be reported when both are documented.

  Full comparison: C20 vs C49.A →

Relationships are read from this code's own official notes, its laterality siblings and its encounter family; the wording of each distinction is MedCoder editorial, and the documentation named in each “what moves you there” line is the official note phrase or sibling title itself. Source: CMS ICD-10-CM tabular instructional notes; ICD-10-CM Official Guidelines, Section I.A.12.a.

Verify Before Coding

• CC as a secondary diagnosis (FY2027). Can raise the stay's MS-DRG severity tier.

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

MedCoder structured relationships — computed from published CMS and AHRQ datasets

Other codes that name C20 or its code family, from the CMS Table of Neoplasms and the CMS Table of Neoplasms (site match derived from the code title).

Referenced by 5 Same-site neoplasm codes: C78.5 — Secondary malignant neoplasm of large intestine and rectumCompare C20 vs C78.5 →, D01.2 — Carcinoma in situ of rectumCompare C20 vs D01.2 →, D12.8 — Benign neoplasm of rectumCompare C20 vs D12.8 →, D37.5 — Neoplasm of uncertain behavior of rectumCompare C20 vs D37.5 →, D49.0 — Neoplasm of unspecified behavior of digestive systemCompare C20 vs D49.0 →.

These codes represent related neoplasm behaviors affecting the same anatomic site.

Referenced by 4 Screening & history codes: Z12.12 — Encounter for screening for malignant neoplasm of rectumCompare C20 vs Z12.12 →, Z85.04 — Personal history of malignant neoplasm of rectum, rectosigmoid junction, and anusCompare C20 vs Z85.04 →, Z85.040 — Personal history of malignant carcinoid tumor of rectumCompare C20 vs Z85.040 →, Z85.048 — Personal history of other malignant neoplasm of rectum, rectosigmoid junction, and anusCompare C20 vs Z85.048 →.

These codes represent screening tests and history codes that refer to this active disease condition.

MS-DRG Grouper Relationships (FY2027)

Potential MS-DRG participation — not a DRG assignment.

FY2027 MS-DRG: CC — Complication or Comorbidity. Reported as a secondary diagnosis, this code raises the stay's MS-DRG severity tier — except when the principal diagnosis is one of 22 clinically related codes on its CMS exclusion list.

Named in the grouper logic of 3 MS-DRGs: DRG 374 (MDC 06), DRG 375 (MDC 06), DRG 376 (MDC 06).

From the CMS MS-DRG Definitions Manual (Appendices B and C). Actual DRG assignment depends on the complete claim.

Clinical classification (AHRQ CCSR):NEO015 — Gastrointestinal cancers - colorectal (default).

Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality.

Related Codes

Same clinical process (MS-DRG)

Acts as CC — raises the severity of other admissions. CMS groups these diagnoses into one MS-DRG principal-diagnosis exclusion process — a CC/MCC on this list never raises severity when the principal diagnosis is also on it.

C21.2 — Malignant neoplasm of cloacogenic zone, C21.8 — Malignant neoplasm of overlapping sites of rectum, anus and anal canal, C26.0 — Malignant neoplasm of intestinal tract, part unspecified, C26.9 — Malignant neoplasm of ill-defined sites within the digestive system, C45.7 — Mesothelioma of other sites, C45.9 — Mesothelioma, unspecified, C46.4 — Kaposi's sarcoma of gastrointestinal sites, C76.8 — Malignant neoplasm of other specified ill-defined sites, C7A.00 — Malignant carcinoid tumor of unspecified site, C7A.026 — Malignant carcinoid tumor of the rectum, C7A.098 — Malignant carcinoid tumors of other sites, C7A.1 — Malignant poorly differentiated neuroendocrine tumors, C7A.8 — Other malignant neuroendocrine tumors, C7B.00 — Secondary carcinoid tumors, unspecified site, C7B.1 — Secondary Merkel cell carcinoma, C80.0 — Disseminated malignant neoplasm, unspecified, C80.1 — Malignant (primary) neoplasm, unspecified, D49.0 — Neoplasm of unspecified behavior of digestive system, D49.81 — Neoplasm of unspecified behavior of retina and choroid, D49.89 — Neoplasm of unspecified behavior of other specified sites, +1 more

Same CMS-HCC risk category (V28)

CMS maps these diagnoses to the same Hierarchical Condition Category (Bladder, Colorectal, and Other Cancers) for risk-adjusted payment.

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 junction, C21.0 — Malignant neoplasm of anus, unspecified, C21.1 — Malignant neoplasm of anal canal, C21.2 — Malignant neoplasm of cloacogenic zone, C21.8 — Malignant neoplasm of overlapping sites of rectum, anus and anal canal, C26.0 — Malignant neoplasm of intestinal tract, part unspecified, C26.1 — Malignant neoplasm of spleen, C26.9 — Malignant neoplasm of ill-defined sites within the digestive system, C51.0 — Malignant neoplasm of labium majus, C51.1 — Malignant neoplasm of labium minus, C51.2 — Malignant neoplasm of clitoris, +105 more

Related risk categories

These categories interact through CMS's HCC hierarchy — one can suppress the other's risk-adjustment weight when both are present on a claim.

Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic, Cancer Metastatic to Bone, Other and Unspecified Metastatic Cancer; Acute Leukemia Except Myeloid, Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers, Lung and Other Severe Cancers, Lymphoma and Other Cancers, Prostate, Breast, and Other Cancers and Tumors

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical category (Gastrointestinal cancers - colorectal).

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 junction, C26.0 — Malignant neoplasm of intestinal tract, part unspecified, C49.A4 — Gastrointestinal stromal tumor of large intestine, C49.A5 — Gastrointestinal stromal tumor of rectum, D01.0 — Carcinoma in situ of colon, D01.1 — Carcinoma in situ of rectosigmoid junction, D01.2 — Carcinoma in situ of rectum, D01.40 — Carcinoma in situ of unspecified part of intestine

Lab tests where this diagnosis supports Medicare coverage (NCD)

Medicare's National Coverage Determination (NCD) program lists this diagnosis as medical justification for these lab tests.

CEA Test, Fecal Occult Blood Test (FOBT), Gamma-glutamyl Transferase (GGT) Test, Iron Panel

Contextual Map

Every relationship of C20 in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Run C20 with these 3 related codes in Claim Check

Hierarchy

• C00-D49 — Chapter 2: Neoplasms (C00-D49) (C00-D49)[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• C00-C75 — Malignant neoplasms, stated or presumed to be primary (of specified sites), and certain specified histologies, except neuroendocrine, and of lymphoid, hematopoietic and related tissue[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026

Excludes1

• C46.4 — Kaposi's sarcoma of gastrointestinal sites[Excludes1]: “Kaposi's sarcoma of gastrointestinal sites (C46.4)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
• C7A.026 — Malignant carcinoid tumor of the rectum[Excludes1]: “malignant carcinoid tumor of the rectum (C7A.026)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Excludes2

• C49.A — Gastrointestinal stromal tumor[Excludes2]: “gastrointestinal stromal tumors (C49.A-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Same site

• C78.5 — Secondary malignant neoplasm of large intestine and rectum[Same site]: “Same site — secondary malignancy (rectum)”— CMS Table of Neoplasms · icd10cm-fy2026
• D01.2 — Carcinoma in situ of rectum[Same site]: “Same site — carcinoma in situ (rectum)”— CMS Table of Neoplasms · icd10cm-fy2026
• D12.8 — Benign neoplasm of rectum[Same site]: “Same site — benign neoplasm (rectum)”— CMS Table of Neoplasms · icd10cm-fy2026
• D37.5 — Neoplasm of uncertain behavior of rectum[Same site]: “Same site — uncertain behavior (rectum)”— CMS Table of Neoplasms · icd10cm-fy2026
• D49.0 — Neoplasm of unspecified behavior of digestive system[Same site]: “Same site — unspecified behavior (rectum)”— CMS Table of Neoplasms · icd10cm-fy2026

Referenced by Same-site neoplasm codes

• C78.5 — Secondary malignant neoplasm of large intestine and rectum[Same site]: “Same site — primary malignancy (rectum)”— CMS Table of Neoplasms · icd10cm-fy2026
• D01.2 — Carcinoma in situ of rectum[Same site]: “Same site — primary malignancy (rectum)”— CMS Table of Neoplasms · icd10cm-fy2026
• D12.8 — Benign neoplasm of rectum[Same site]: “Same site — primary malignancy (rectum)”— CMS Table of Neoplasms · icd10cm-fy2026
• D37.5 — Neoplasm of uncertain behavior of rectum[Same site]: “Same site — primary malignancy (rectum)”— CMS Table of Neoplasms · icd10cm-fy2026
• D49.0 — Neoplasm of unspecified behavior of digestive system[Same site]: “Same site — primary malignancy (rectum)”— CMS Table of Neoplasms · icd10cm-fy2026

Referenced by Screening & history codes MedCoder-derived

• Z12.12 — Encounter for screening for malignant neoplasm of rectum[Lifecycle]: “Active disease for this site (rectum)”— CMS Table of Neoplasms (site match derived from the code title) · icd10cm-fy2026
• Z85.04 — Personal history of malignant neoplasm of rectum, rectosigmoid junction, and anus[Lifecycle]: “Active disease for this site (rectum)”— CMS Table of Neoplasms (site match derived from the code title) · icd10cm-fy2026
• Z85.040 — Personal history of malignant carcinoid tumor of rectum[Lifecycle]: “Active disease for this site (rectum)”— CMS Table of Neoplasms (site match derived from the code title) · icd10cm-fy2026
• Z85.048 — Personal history of other malignant neoplasm of rectum, rectosigmoid junction, and anus[Lifecycle]: “Active disease for this site (rectum)”— CMS Table of Neoplasms (site match derived from the code title) · icd10cm-fy2026

Clinical classification (CCSR)

• NEO015 — Gastrointestinal cancers - colorectal[CCSR]— AHRQ CCSR for ICD-10-CM Diagnoses (HCUP)

Risk adjustment (CMS-HCC)

• HCC 22 — Bladder, Colorectal, and Other Cancers [CMS-HCC]: “Bladder, Colorectal, and Other Cancers — supersedes HCC 23 (Prostate, Breast, and Other Cancers and Tumors)”— CMS-HCC V28 · 2026

MS-DRG Grouper

• CC — Complication or Comorbidity [MS-DRG severity]: “As a secondary diagnosis this code can raise the stay's MS-DRG severity tier (CC).”— CMS MS-DRG Definitions Manual (Appendix C) · FY2027
• DRG 374 — DIGESTIVE MALIGNANCY WITH MCC[MS-DRG]: “DIGESTIVE MALIGNANCY WITH MCC (MDC 06)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2027
• DRG 375 — DIGESTIVE MALIGNANCY WITH CC[MS-DRG]: “DIGESTIVE MALIGNANCY WITH CC (MDC 06)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2027
• DRG 376 — DIGESTIVE MALIGNANCY WITHOUT CC/MCC[MS-DRG]: “DIGESTIVE MALIGNANCY WITHOUT CC/MCC (MDC 06)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2027

MDC crossing

• MDC 06 — Diseases and Disorders of the Digestive System[MDC crossing]: “Diseases and Disorders of the Digestive System — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs. 5,748 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2027

Neoplasm sites

• Neoplasm, neoplastic, rectum (ampulla) — Neoplasm, neoplastic, rectum (ampulla) — Malignant, Primary [Neoplasm table]: “Neoplasm, neoplastic, rectum (ampulla) (Malignant, Primary)”— CMS Table of Neoplasms · icd10cm-fy2026

Change history

• FY2016 — In the code set at ICD-10-CM adoption [Change history]— CMS release files (code change ledger) · icd10cm-fy2016

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data

CMS/CDC ICD-10-CM FY2027 tabular list, index and tables, effective October 1, 2026 Release, file and checksum · Publisher’s page

Claim edits Official source data

CMS Definitions of Medicare Code Edits — v44.0 (October 2026) Release, file and checksum · Publisher’s page

Inpatient payment groups Official source data

CMS MS-DRG Definitions Manual (incl. Appendix B diagnosis index, Appendix C CC/MCC list, Appendix E procedure index) and IPPS Final Rule tables — v44 Release, file and checksum · Publisher’s page

Risk adjustment Official source data

2026 Mid-Year Final ICD-10 Mappings + Model Software (cms.gov/files/zip/2026-midyear-final-icd-10-mappings.zip, 2026-midyear-final-model-software.zip) — CMS-HCC V28, PY2026 mid-year final release Release, file and checksum · Publisher’s page

Change history and date-of-service validity Official source data

CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page

Comparisons, relationships and the contextual map MedCoder structured relationship

Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears

Summary and FAQ answers MedCoder explanation

Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates