What is ICD-10 code C19?

C19 is the ICD-10-CM diagnosis code for Malignant neoplasm of rectosigmoid junction. Cancer that occurs at the rectosigmoid junction, which is the area where the sigmoid colon meets the rectum. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C19 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C19 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. C19 is a payment HCC under the CMS risk adjustment model. Under the CMS-HCC V28 risk adjustment model it maps to Bladder, Colorectal, and Other Cancers with a community, non-dual, aged base RAF weight of 0.363. Under the older CMS-HCC V24 model it maps to Colorectal, Bladder, and Other Cancers at RAF 0.307. V28 reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition. HCC Buddy maintains the V28 and V24 mapping, RAF weight, and MEAT documentation criteria for C19 sourced directly from the CMS-HCC model files.

Yes. C19 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. C19 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

What is the V28 vs V24 difference for C19?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. For C19, V28 maps to Bladder, Colorectal, and Other Cancers at RAF 0.363 while V24 mapped to Colorectal, Bladder, and Other Cancers at RAF 0.307. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting C19?

This code is used when the tumor involves the junction between sigmoid colon and rectum Verify documentation confirms involvement of the junction area rather than just one segment Because C19 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

C19: Malignant neoplasm of rectosigmoid junction — ICD-10 | Bladder, Colorectal, and Other

ICD-10-CM Code View

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Code lookupC19Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of digestive organs (C15-C26)

C19

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Malignant neoplasm of rectosigmoid junction

Cancer that occurs at the rectosigmoid junction, which is the area where the sigmoid colon meets the rectum.

Buddy Insight

CMS-HCC V28

Mapped

HCC 22

Bladder, Colorectal, and Othe...

RAF 0.363

CMS-HCC V24

Mapped

HCC 11

Colorectal, Bladder, and Othe...

RAF 0.307

ACA/HHS

Mapped

HCC 11

HHS-HCC 11

Varies by metal level

ESRD/PACE

Mapped

HCC 11

Colorectal, Bladder, and Othe...

RAF 0.059

RXHCC

N/A

—

Not risk-adjusted for this model/period.

Not mapped

Code Book Path

Official

C1Malignant neoplasms of digestive organs (C15-C26)

C19Malignant neoplasm of rectosigmoid junction

Inclusion Terms

Official

Malignant neoplasm of colon with rectum
Malignant neoplasm of rectosigmoid (colon)

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C19 in this effective period.

Related Child Codes

Official

ICD-10-CM does not list child codes under C19 for this display context.

Includes

Official

ICD-10-CM does not list Includes notes for C19 in this effective period.

Excludes 1

Official

malignant carcinoid tumors of the colon (C7A.02-)

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C19 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C19 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C19 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Documentation confirming the tumor involves the rectosigmoid junction specifically

Distance from the anal verge if measured (typically 12-15 cm)

Histological type and grade

Stage of disease with circumferential resection margin status

MEAT Support

HCC Buddy guidance

Documentation confirming the tumor involves the rectosigmoid junction specifically

Distance from the anal verge if measured (typically 12-15 cm)

Histological type and grade

Stage of disease with circumferential resection margin status

Audit Caution

HCC Buddy guidance

Coding as sigmoid (C18.7) or rectal (C20) when the tumor actually spans the junction between the two

Not recognizing that 'low sigmoid' and 'upper rectal' descriptions may actually represent rectosigmoid junction tumors

Failing to distinguish C19 (junction) from C18.8 (overlapping colon sites) — C19 is a single specific location, not overlapping sites

Common Mistakes

HCC Buddy guidance

C18.7 — Sigmoid colon: if the tumor is entirely in the sigmoid without extending to the rectum, use C18.7

C20 — Rectum: if the tumor is entirely rectal without sigmoid extension, use C20

C21.8 — Overlapping sites of rectum/anus/anal canal: use when the tumor extends below the rectum to involve anal structures

Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.

Is C19 an HCC code?

Yes. C19 maps to Bladder, Colorectal, and Other Cancers under the CMS-HCC V28 risk adjustment model (and Colorectal, Bladder, and Other Cancers under V24).

HCC Category Mapping

V28HCC 22, Bladder, Colorectal, and Other Cancers

0.363

V24HCC 11, Colorectal, Bladder, and Other Cancers

0.307

ESRDHCC 11, Colorectal, Bladder, and Other Cancers

0.059

Each model's RAF is its CMS base weight for that model's standard population, so weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.

Work C19 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for C19

For C19to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.

MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
EEvaluate: test results, medication response, or physical findings reviewed by the provider
AAssess: explicit mention in the assessment or plan with acknowledgment of status
TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis

Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed C19 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

C19 is the ICD-10-CM diagnosis code for malignant neoplasm of rectosigmoid junction. Cancer that occurs at the rectosigmoid junction, which is the area where the sigmoid colon meets the rectum. C19 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of digestive organs (c15-c26).

Under the CMS-HCC V28 risk adjustment model, C19 maps to Bladder, Colorectal, and Other Cancers (HCC 22) with a community, non-dual, aged base RAF weight of 0.363. Under the older CMS-HCC V24 model, C19 maps to Colorectal, Bladder, and Other Cancers (HCC 11) with a community, non-dual, aged base RAF weight of 0.307. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.

This code is used when the tumor involves the junction between sigmoid colon and rectum. Because C19 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.

HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for C19 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•This code is used when the tumor involves the junction between sigmoid colon and rectum
•Verify documentation confirms involvement of the junction area rather than just one segment

Clinical Significance

Malignant neoplasm of the rectosigmoid junction is clinically significant because tumors at this boundary zone between the sigmoid colon and rectum may require treatment approaches from both colon and rectal cancer paradigms. The rectosigmoid junction is defined as the area approximately 12-15 cm from the anal verge, and cancers here may be managed with either low anterior resection or sigmoid colectomy depending on exact location and extent. Accurate coding at this specific junction affects treatment decisions and resource allocation.

Documentation Requirements

✓Documentation confirming the tumor involves the rectosigmoid junction specifically
✓Distance from the anal verge if measured (typically 12-15 cm)
✓Histological type and grade
✓Stage of disease with circumferential resection margin status
✓Whether neoadjuvant chemoradiation was administered (more common for rectal-predominant tumors)

Excludes 1, Do NOT code together

malignant carcinoid tumors of the colon (C7A.02-)

Commonly Confused Codes

•C18.7: Sigmoid colon: if the tumor is entirely in the sigmoid without extending to the rectum, use C18.7
•C20: Rectum: if the tumor is entirely rectal without sigmoid extension, use C20
•C21.8: Overlapping sites of rectum/anus/anal canal: use when the tumor extends below the rectum to involve anal structures

Code Hierarchy

└C19Malignant neoplasm of rectosigmoid junction

C19 ICD-10-CM Code: Malignant neoplasm of rectosigmoid junction

HCC Buddy Code Card

C19

Is C19 an HCC code?

HCC Category Mapping

MEAT Criteria for C19

Get the V28 RAF + MEAT cheat sheet

What This Code Means

Coding Tips

Clinical Significance

Documentation Requirements

Excludes 1, Do NOT code together

Commonly Confused Codes

Code Hierarchy

Work C19 in HCC Buddy