2026 ICD-10-CM Diagnosis Code Z51.11Encounter for antineoplastic chemotherapy

ICD-10-CM Codes›Z00–Z99›Z40-Z53›Z51

ICD-10-CM Z51.11
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

Z51.11 is a billable ICD-10-CM diagnosis code for encounter for antineoplastic chemotherapy. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 826 through 830, 837 through 839, 846 through 848. The code is exempt from POA reporting. Coders also document this condition as chemotherapy AND/OR radiation therapy prior to lymphadenectomy. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Encounter for antineoplastic therapies.

Code Identity

ICD-10-CM Code
Z51.11
Billable Status
Yes — Valid for Submission
Code Describes
Encounter for antineoplastic chemotherapy
Short Description
Encounter for antineoplastic chemotherapy
Same as the full description in the CMS dataset.
Parent Code
Z51.1
Encounter for antineoplastic chemotherapy and immunotherapy

Code Classification

ChapterZ00–Z99Factors influencing health status and contact with health services
SectionZ40-Z53Encounters for other specific health care
CategoryZ51Encounter for other aftercare and medical care
This CodeZ51.11Encounter for antineoplastic chemotherapy

Present on Admission (POA)Billing

Z51.11 is exempt from POA reporting on inpatient claims to general acute care hospitals. Review other POA exempt codes.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Chemotherapy AND/OR radiation therapy prior to lymphadenectomy
  • Chemotherapy changed - patient choice
  • Chemotherapy changed - progressive disease during chemotherapy
  • Chemotherapy changed - technical or organizational problems
  • Chronic disease - treatment changed
  • Reason for change in planned chemotherapy treatment

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Chemotherapy(session) (for)
      • cancer
    • Chemotherapy(session) (for)
      • neoplasm
    • Encounter(with health service) (for)
      • chemotherapy for neoplasm
    • Maintenance(encounter for)
      • antineoplastic chemotherapy

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR FAC006
Encounter for antineoplastic therapies
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Cancer Chemotherapy

Cancer chemotherapy is a type of cancer treatment. It uses medicines to destroy cancer cells.

The full article covers:

  • What is cancer chemotherapy?
  • What are the side effects of chemotherapy?
  • What can I expect when getting chemotherapy?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert Z51.11 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
V58.11 Antineoplastic chemo enc
Exact Match The mapping is direct, with no qualifiers.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About Z51.11Overview

Is Z51.11 (Encounter for antineoplastic chemotherapy and immunotherapy) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report encounter for antineoplastic chemotherapy on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does Z51.11 group to?

When encounter for antineoplastic chemotherapy is the principal diagnosis on an inpatient stay, it groups to MS-DRG 826, 827, 828, 829, 830, 837, 838, 839, 846, 847, 848, with relative weights from 0.8494 to 4.8043 depending on complications. Higher weights mean higher Medicare reimbursement.

Is Z51.11 exempt from POA reporting?

Yes. CMS lists this code among those exempt from present on admission reporting, so hospitals do not assign a POA indicator for encounter for antineoplastic chemotherapy on inpatient claims.

What is the ICD-9 equivalent of Z51.11?

Under the General Equivalence Mappings, encounter for antineoplastic chemotherapy converts to ICD-9-CM V58.11 (antineoplastic chemo enc). The mapping is a direct match.