ICD-10 Code for Colorectal Cancer: Complete Guide to Diagnosis and Coding

When documentation specifies “colon cancer” or “rectal cancer,” it seems clear to code colorectal cancer. However, in actual clinical billing, the proper ICD-10 Code for Colorectal Cancer is determined by the reported anatomic site, if the malignancy is ongoing or historical, if metastatic disease is present and the cause for the encounter. An improper or missing code can lead to denial of claims, medical-necessity revisions, wrong reimbursement, delayed payment, documentation inquiries and audit risk.

This guide provides key ICD-10-CM codes for colorectal cancers, key metastatic and history codes, documentation requirements, and CPT procedures frequently connected with them. It also shows why diagnoses like colon cancer ICD 10, rectal cancer ICD 10 and sigmoid colon cancer ICD 10 should not be considered interchangeable diseases.

What Is the ICD-10 Code for Colorectal Cancer?

There is not a single ICD-10-CM code that encompasses all diagnoses of colorectal cancer. The correct code is chosen based on the documented site.

For example, C18.9 is malignant tumor of colon, nonspecific, C18.7 is malignant neoplasm of sigmoid colon. C20 is malignant tumor of the rectum, whereas C19 is malignant neoplasm of the rectosigmoid junction.

Therefore, coders should not automatically report C18.9 whenever the record contains the general phrase “colorectal cancer.” The medical record should be reviewed for the most specific documented site.

2026 ICD-10-CM Code Set and Effective Dates

For contacts that happen between April 1 2026 and September 30 2026 CMS says that the ICD-10-CM files from April 1 2026 are the ones that apply for FY 2026. The ICD-10-CM code set, for FY 2027 will be used starting on October 1 2026. Will continue until September 30 2027.

This is useful for rectifying claims, auditing historical records, or updating coding software. The diagnosis code should be the same as the code set in effect on the date of service or other applicable coding date.

Master ICD-10 Reference Table for Colorectal Cancer

Condition or Scenario	ICD-10-CM Code	Official Description
Colon cancer, unspecified site	C18.9	Malignant neoplasm of colon, unspecified
Cecal cancer	C18.0	Malignant neoplasm of cecum
Ascending colon cancer	C18.2	Malignant neoplasm of ascending colon
Transverse colon cancer	C18.4	Malignant neoplasm of transverse colon
Descending colon cancer	C18.6	Malignant neoplasm of descending colon
Sigmoid colon cancer	C18.7	Malignant neoplasm of sigmoid colon
Overlapping sites of colon	C18.8	Malignant neoplasm of overlapping sites of colon
Rectosigmoid cancer	C19	Malignant neoplasm of rectosigmoid junction
Rectal cancer	C20	Malignant neoplasm of rectum
Secondary liver malignancy	C78.7	Secondary malignant neoplasm of liver and intrahepatic bile duct
Personal history of large-intestine malignancy	Z85.038	Personal history of other malignant neoplasm of large intestine

The C18 category contains site-specific colon malignancies, including sigmoid colon cancer, while C19 and C20 distinguish the rectosigmoid junction and rectum.

Active Cancer vs. Personal History

One of the most important billing distinctions is whether the cancer is still an active condition or has been treated and is now documented as a personal history.

For example, Z85.038 describes a personal history of other malignant neoplasm of the large intestine. When the malignancy is no longer active, a history code may be appropriate rather than an active C18-C20 malignancy code. Follow-up encounters also require attention to the applicable Z08 sequencing guidance.

Do not change an active malignancy to a history code simply because the patient is currently receiving surveillance. Review the provider’s documentation and the reason for the encounter.

How to Select the Correct Colorectal Cancer Code

1. Start With the Provider’s Diagnosis

The coder should begin with the provider’s documented diagnosis rather than independently diagnosing cancer from a pathology report, imaging study, colonoscopy finding, or laboratory result.

Documentation such as “adenocarcinoma of sigmoid colon” supports a site-specific diagnosis. Documentation that only says “colon cancer” may support C18.9 when no additional provider documentation establishes a more specific site.

2. Identify the Anatomic Site

Determine whether the malignancy involves the:

• Cecum
• Ascending colon
• Transverse colon
• Descending colon
• Sigmoid colon
• Rectosigmoid junction
• Rectum

This distinction directly affects code selection. For example, C18.7 is the ICD-10-CM code for malignant neoplasm of sigmoid colon, whereas C20 is used for malignant neoplasm of rectum.

3. Do Not Confuse Rectosigmoid With Sigmoid or Rectal Cancer

The documentation must explicitly state that the rectosigmoid junction is coded as C19. It should not automatically use C18.7 or C20. The C19 code is used to describe a neoplasm located at the rectosigmoid junction.

If the documentation is unclear use the organization’s provider‑query process instead of guessing the site.

4. Determine Whether Metastatic Disease Is Documented

Colorectal cancer can spread to distant organs. When secondary malignancy is documented, additional diagnosis coding may be required according to the applicable coding guidelines and encounter circumstances.

For example, C78.7 identifies secondary malignant neoplasm of the liver and intrahepatic bile duct.

The primary colorectal malignancy and documented metastatic sites should be evaluated separately; a metastatic site does not automatically replace the primary cancer code.

5. Review the Reason for the Encounter

The diagnosis sequence can differ depending on whether the diagnosis sequence’s being applied to a patient who is being treated for an active malignancy receiving cancer‑related therapy under surveillance after completed treatment or being evaluated for another condition.

The claim should reflect the documented reason for the service and applicable ICD-10-CM sequencing rules—not simply the patient’s most serious historical diagnosis.

CPT and Billing Codes Commonly Associated With Colorectal Cancer Care

ICD-10-CM codes describe diagnoses; CPT codes describe services and HCPCS codes describe services, procedures and supplies. A colorectal cancer claim may contain an ICD-10-CM diagnosis code and one or more CPT or HCPCS procedure codes.

Common CPT services encountered in colorectal evaluation and treatment include:

Service	Common CPT Code(s)
Diagnostic colonoscopy	45378
Colonoscopy with biopsy	45380
Colonoscopy with submucosal injection	45381
Colonoscopy with control of bleeding	45382
Colonoscopy with lesion removal by hot biopsy forceps	45384
Colonoscopy with snare removal	45385

These are examples of frequently encountered procedure codes, not a complete colorectal cancer CPT list. Code selection depends on what the physician actually performed and documented. CMS materials identify these colonoscopy codes among services used for colonoscopy procedures with or without biopsy, injection, bleeding control, and lesion removal.

NCCI edits also matter. For example, CMS explains that 45385 and 45380 may be reported together in appropriate circumstances when separate lesions are involved, with the appropriate modifier when the NCCI requirements are satisfied. A modifier should never be added merely to bypass an edit.

For cancer treatment CPT and HCPCS codes might be needed for surgery anesthesia, pathology, radiation oncology, chemotherapy administration, immunotherapy, drugs, imaging and lab services. These codes need to be chosen from the CPT/HCPCS code lists based on the real service that was done.

Documentation Checklist for Colorectal Cancer Billing

Strong documentation improves code specificity, medical necessity support, claim accuracy, and audit defensibility.

Documentation Element	Why It Matters
Confirmed diagnosis	Establishes the condition being treated or evaluated
Exact anatomic site	Supports the most specific C18-C20 code
Primary vs. secondary malignancy	Prevents incorrect sequencing and diagnosis assignment
Active vs. historical cancer	Helps distinguish C-category malignancy codes from history coding
Metastatic sites	Supports separately documented secondary malignancies
Current treatment status	Helps establish the purpose of the encounter
Procedure performed	Supports accurate CPT reporting
Pathology and operative documentation	May clarify the documented diagnosis and site
Reason for encounter	Supports appropriate diagnosis sequencing
Medical necessity	Helps support procedures, treatments, and payer review

Coders should use the provider’s documentation and follow official coding guidance when determining whether clarification is necessary.

Common Colorectal Coding Mistakes

Using C18.9 When a Specific Site Is Documented

If the provider documents sigmoid colon cancer, C18.7 is more specific than unspecified colon cancer.

Treating All “Colorectal Cancer” as Colon Cancer

Rectal malignancy is separately represented by C20, while rectosigmoid junction malignancy is represented by C19.

Coding a History of Cancer as Active Cancer

A patient with a documented personal history of treated large-intestine cancer should not automatically receive an active C18-C20 malignancy code. Review the current clinical status and reason for the encounter.

Confusing Related Cancer Keywords

Search terms such as gastric cancer ICD 10 and pancreatic cancer ICD 10 refer to different malignancies and should not be substituted for a colorectal diagnosis. Likewise, colon cancer ICD 10 and rectal cancer ICD 10 require site-specific consideration.

Conclusion

Accurate ICD‑10 Code for cancer selection requires more than simply matching the phrase “colorectal cancer” to a code. The coder must first establish the documented site distinguish colon from rectum and rectosigmoid junction. The coder must also determine whether the malignancy is active or historical review documented disease and connect the diagnosis to the service being billed with the correct ICD‑10 Code.

For billing teams this level of specificity matters because diagnosis coding supports necessity, claim accuracy, reimbursement and audit defensibility. Always verify the ICD‑10 Code, CPT, HCPCS, NCCI, CMS and payer requirements for the patient’s date of service before submitting a claim. CMS maintains the current ICD‑10 Code files and effective‑date information, for each year.

FAQ: ICD-10 Code for Colorectal Cancer

What is the most common ICD-10 code for colon cancer?

When the provider documents colon cancer without a more specific site, C18.9 represents malignant neoplasm of colon, unspecified. When the site is documented, a more specific C18 code should generally be considered.

What is the ICD-10 code for sigmoid colon cancer?

C18.7 — Malignant neoplasm of sigmoid colon.

What is the rectal cancer ICD 10 code?

C20 — Malignant neoplasm of rectum.

What is the ICD-10 code for rectosigmoid cancer?

C19 — Malignant neoplasm of rectosigmoid junction.

Is there one ICD-10 code for all colorectal cancer?

No. Coding depends primarily on the documented anatomic site, disease status, metastatic involvement, and purpose of the encounter.