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Chapter 2: Neoplasms (C00-D49) General Guidelines
Comprehensive ICD-10-CM coding guidelines for neoplasms, covering benign, malignant, and metastatic conditions
Foundation
Understanding Neoplasm Coding
Chapter 2 of the ICD-10-CM contains the codes for most benign and all malignant neoplasms. Certain benign neoplasms, such as prostatic adenomas, may be found in the ICD-10-CM Official Guidelines for Coding and Reporting FY 2026 Page 33 of 121 specific body system chapters. To properly code a neoplasm, it is necessary to determine from the record if the neoplasm is benign, in-situ, malignant, or of uncertain histologic behavior. If malignant, any secondary (metastatic) sites should also be determined.
Primary Malignant Neoplasms Overlapping Site Boundaries
A primary malignant neoplasm that overlaps two or more contiguous (next to each other) sites should be classified to the subcategory/code .8 ('overlapping lesion'), unless the combination is specifically indexed elsewhere. For multiple neoplasms of the same site that are not contiguous such as tumours in different quadrants of the same breast, codes for each site should be assigned.
Malignant Neoplasm of Ectopic Tissue
Malignant neoplasms of ectopic tissue are to be coded to the site of origin mentioned, e.g., ectopic pancreatic malignant neoplasms involving the stomach are coded to malignant neoplasm of pancreas, unspecified (C25.9).
See Section I.C.21. Factors influencing health status and contact with health services, Status, for information regarding Z15.0, codes for genetic susceptibility to cancer.
a. Admission/Encounter for Treatment of Primary Site
If the malignancy is chiefly responsible for occasioning the patient admission/encounter and treatment is directed at the primary site, designate the primary malignancy as the principal/first-listed diagnosis. The only exception to this guideline is if the administration of chemotherapy, immunotherapy or external beam radiation therapy is chiefly responsible for occasioning the admission/encounter. In that case, assign the appropriate Z51.-- code as the first-listed or principal diagnosis, and the underlying diagnosis or problem for which the service is being performed as a secondary diagnosis.
b. Admission/Encounter for Treatment of Secondary Site
When a patient is admitted because of a primary neoplasm with metastasis and treatment is directed toward the secondary site only, the secondary neoplasm is ICD-10-CM Official Guidelines for Coding and Reporting FY 2026 Page 34 of 121 designated as the principal diagnosis even though the primary malignancy is still present.
c. Coding and Sequencing of Complications
Coding and sequencing of complications associated with the malignancies or with the therapy thereof are subject to the following guidelines:
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Guideline 1
Anaemia Associated with Malignancy
1
Anaemia Associated with Malignancy
When admission/encounter is for management of an anaemia associated with the malignancy, and the treatment is only for anaemia, the appropriate code for the malignancy is sequenced as the principal or first-listed diagnosis followed by the appropriate code for the anaemia (such as code D63.0, Anaemia in neoplastic disease).
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Guideline 2
Anaemia Associated with Chemotherapy, Immunotherapy and Radiation Therapy
01
Chemotherapy/Immunotherapy-Related Anaemia
When the admission/encounter is for management of an anaemia associated with an adverse effect of the administration of chemotherapy or immunotherapy and the only treatment is for the anaemia, the anaemia code is sequenced first followed by the appropriate codes for the neoplasm and the adverse effect (T45.1X5-, Adverse effect of antineoplastic and immunosuppressive drugs).
02
Radiotherapy-Related Anaemia
When the admission/encounter is for management of an anaemia associated with an adverse effect of radiotherapy, the anaemia code should be sequenced first, followed by the appropriate neoplasm code and code Y84.2, Radiological procedure and radiotherapy as the cause of abnormal reaction of the patient, or of later complication, without mention of misadventure at the time of the procedure.
Critical Sequencing Rule: For treatment-related anaemia, the anaemia code is sequenced first, unlike malignancy-associated anaemia where the malignancy comes first.
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Guideline 3
Management of Dehydration Due to the Malignancy
Sequencing Rule
When the admission/encounter is for management of dehydration due to the malignancy and only the dehydration is being treated (intravenous rehydration), the dehydration is sequenced first, followed by the code(s) for the malignancy.
Dehydration Code
Primary diagnosis
Malignancy Code
Secondary diagnosis
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Guideline 4
Treatment of a Complication Resulting from a Surgical Procedure
When the admission/encounter is for treatment of a complication resulting from a surgical procedure, designate the complication as the principal or first-listed diagnosis if treatment is directed at resolving the complication.
d. Primary Malignancy Previously Excised
When a primary malignancy has been previously excised or eradicated from its site and there is no further treatment directed to that site and there is no evidence of any existing primary malignancy at that site, a code from category Z85, ICD-10-CM Official Guidelines for Coding and Reporting FY 2026 Page 35 of 121 Personal history of malignant neoplasm, should be used to indicate the former site of the malignancy. Any mention of extension, invasion, or metastasis to another site is coded as a secondary malignant neoplasm to that site. The secondary site may be the principal or first-listed diagnosis with the Z85 code used as a secondary code.
See section I.C.2.t. Secondary malignant neoplasm of lymphoid tissue.
e. Admissions/Encounters Involving Antineoplastic Chemotherapy, Immunotherapy and Radiation Therapy
Z85 Code Usage
Use Z85 codes when primary malignancy has been excised, no further treatment is directed to that site, and no evidence of existing primary malignancy remains at that site.
Secondary Neoplasm Coding
Any extension, invasion, or metastasis to another site is coded as a secondary malignant neoplasm. The secondary site may be principal diagnosis with Z85 as secondary code.
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Guideline 5
Episode of Care Involves Surgical Removal of Neoplasm
5
Surgical Removal + Adjunct Therapy
When an episode of care involves the surgical removal of a neoplasm, primary or secondary site, followed by adjunct chemotherapy or radiation treatment during the same episode of care, the code for the neoplasm should be assigned as principal or first-listed diagnosis.
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Guideline 6
Patient Admission/Encounter Chiefly for Administration of Antineoplastic Therapy
If a patient admission/encounter is chiefly for the administration of chemotherapy, immunotherapy or external beam radiation therapy for the treatment of a neoplasm, assign code Z51.0, Encounter for antineoplastic radiation therapy, or Z51.11, Encounter for antineoplastic chemotherapy, or Z51.12, Encounter for antineoplastic immunotherapy as the first-listed or principal diagnosis.
Z51.0
Encounter for antineoplastic radiation therapy
Z51.11
Encounter for antineoplastic chemotherapy
Z51.12
Encounter for antineoplastic immunotherapy
If the reason for the encounter is more than one type of antineoplastic therapy, code Z51.0 and codes from subcategory Z51.1 may be assigned together, in which case one of these codes would be reported as a secondary diagnosis. The malignancy for which the therapy is being administered should be assigned as a secondary diagnosis.
Special Case - Brachytherapy: If a patient admission/encounter is for the insertion or implantation of radioactive elements (e.g., brachytherapy) the appropriate code for the malignancy is sequenced as the principal or first-listed diagnosis. Code Z51.0 should not be assigned.
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Guideline 7
Patient Admitted for Therapy and Develops Complications
External Beam Radiotherapy, Immunotherapy or Chemotherapy
When a patient is admitted for the purpose of external beam radiotherapy, immunotherapy or chemotherapy and develops complications such as uncontrolled nausea and vomiting or dehydration, the principal or first-listed diagnosis is Z51.0, Encounter for antineoplastic radiation therapy, or Z51.11, Encounter for antineoplastic chemotherapy, or Z51.12, Encounter for antineoplastic immunotherapy followed by any codes for the complications. ICD-10-CM Official Guidelines for Coding and Reporting FY 2026 Page 36 of 121
Step 1: Z51 Code First
Assign appropriate Z51.0, Z51.11, or Z51.12 as principal diagnosis
Step 2: Complication Codes
Follow with codes for complications (nausea, vomiting, dehydration, etc.)
Brachytherapy (Radioactive Element Insertion/Implantation)
When a patient is admitted for the purpose of insertion or implantation of radioactive elements (e.g., brachytherapy) and develops complications such as uncontrolled nausea and vomiting or dehydration, the principal or first-listed diagnosis is the appropriate code for the malignancy followed by any codes for the complications.
f. Admission/Encounter to Determine Extent of Malignancy
When the reason for admission/encounter is to determine the extent of the malignancy, or for a procedure such as paracentesis or thoracentesis, the primary malignancy or appropriate metastatic site is designated as the principal or first-listed diagnosis, even though chemotherapy or radiotherapy is administered.
g. Symptoms, Signs, and Abnormal Findings Listed in Chapter 18 Associated with Neoplasms
Symptoms, signs, and ill-defined conditions listed in Chapter 18 characteristic of, or associated with, an existing primary or secondary site malignancy cannot be used to replace the malignancy as principal or first-listed diagnosis, regardless of the number of admissions or encounters for treatment and care of the neoplasm.
See section I.C.21. Factors influencing health status and contact with health services, Encounter for prophylactic organ removal.
h. Admission/Encounter for Pain Control/Management
See Section I.C.6. for information on coding admission/encounter for pain control/management.
i. Malignancy in Two or More Noncontiguous Sites
A patient may have more than one malignant tumour in the same organ. These tumours may represent different primaries or metastatic disease, depending on the site. Should the documentation be unclear, the provider should be queried as to the status of each tumour so that the correct codes can be assigned.
j. Disseminated Malignant Neoplasm, Unspecified
Code C80.0, Disseminated malignant neoplasm, unspecified, is for use only in those cases where the patient has advanced metastatic disease and no known primary or secondary sites are specified. It should not be used in place of assigning codes for the primary site and all known secondary sites.
k. Malignant Neoplasm Without Specification of Site
Code C80.1, Malignant (primary) neoplasm, unspecified, equates to Cancer, unspecified. This code should only be used when no determination can be made as to the primary site of a malignancy. This code should rarely be used in the inpatient setting. ICD-10-CM Official Guidelines for Coding and Reporting FY 2026 Page 37 of 121
l. Sequencing of Neoplasm Codes
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Guideline 8
Encounter for Treatment of Primary Malignancy
8
Sequencing Rule
If the reason for the encounter is for treatment of a primary malignancy, assign the malignancy as the principal/first-listed diagnosis. The primary site is to be sequenced first, followed by any metastatic sites.
Primary Malignancy
Principal/first-listed diagnosis
Metastatic Sites
Secondary diagnoses
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Guideline 9
Encounter for Treatment of Secondary Malignancy
Sequencing Rule
When an encounter is for a primary malignancy with metastasis and treatment is directed toward the metastatic (secondary) site(s) only, the metastatic site(s) is designated as the principal/first-listed diagnosis. The primary malignancy is coded as an additional code.
9
1
Metastatic Site(s)
Principal diagnosis
2
Primary Malignancy
Additional code
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Guideline 10
Malignant Neoplasm in a Pregnant Patient
When a pregnant patient has a malignant neoplasm, a code from subcategory O9A.1-, Malignant neoplasm complicating pregnancy, childbirth, and the puerperium, should be sequenced first, followed by the appropriate code from Chapter 2 to indicate the type of neoplasm.
01
First: O9A.1- Code
Malignant neoplasm complicating pregnancy, childbirth, and the puerperium
02
Second: Chapter 2 Code
Appropriate code indicating the specific type of neoplasm
Special Population Consideration: Pregnancy codes take precedence when a malignant neoplasm complicates pregnancy, childbirth, or the puerperium.
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Guideline 11
Encounter for Complication Associated with a Neoplasm
When an encounter is for management of a complication associated with a neoplasm, such as dehydration, and the treatment is only for the complication, the complication is coded first, followed by the appropriate code(s) for the neoplasm.
General Rule
Complication code first, then neoplasm code(s)
Exception: Anaemia
When the admission/encounter is for management of an anaemia associated with the malignancy, and the treatment is only for anaemia, the appropriate code for the malignancy is sequenced as the principal or first-listed diagnosis followed by code D63.0, Anaemia in neoplastic disease.
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Guideline 12
Complication from Surgical Procedure for Treatment of a Neoplasm
Sequencing Rule
When an encounter is for treatment of a complication resulting from a surgical procedure performed for the treatment of the neoplasm, designate the complication as the principal/first-listed diagnosis.
See the guideline regarding the coding of a current malignancy versus personal history to determine if the code for the neoplasm should also be assigned.
Principal Diagnosis
Surgical complication code
Additional Code
Neoplasm code (if applicable based on current vs. history status)
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Guideline 13
Pathologic Fracture Due to a Neoplasm
When an encounter is for a pathological fracture due to a neoplasm, and the focus of treatment is the fracture, a code from subcategory M84.5, Pathological fracture in neoplastic disease, should be sequenced first, followed by the code for the neoplasm.
Focus: Fracture
M84.5 code first, then neoplasm code
Focus: Neoplasm
Neoplasm code first, then M84.5 code
If the focus of treatment is the neoplasm with an associated pathological fracture, the neoplasm code should be sequenced first, followed by a code from M84.5 for the pathological fracture. ICD-10-CM Official Guidelines for Coding and Reporting FY 2026 Page 38 of 121
m. Current Malignancy Versus Personal History of Malignancy
When a primary malignancy has been excised but further treatment, such as an additional surgery for the malignancy, radiation therapy or chemotherapy is directed to that site, the primary malignancy code should be used until treatment is completed.
When a primary malignancy has been previously excised or eradicated from its site, there is no further treatment (of the malignancy) directed to that site, and there is no evidence of any existing primary malignancy at that site, a code from category Z85, Personal history of malignant neoplasm, should be used to indicate the former site of the malignancy.
Codes from subcategories Z85.0 – Z85.85 should only be assigned for the former site of a primary malignancy, not the site of a secondary malignancy. Code Z85.89 may be assigned for the former site(s) of either a primary or secondary malignancy.
See Section I.C.21. Factors influencing health status and contact with health services, History (of)
n. Leukaemia, Multiple Myeloma, and Malignant Plasma Cell Neoplasms in Remission Versus Personal History
The categories for leukaemia, and category C90, Multiple myeloma and malignant plasma cell neoplasms, have codes indicating whether or not the leukaemia has achieved remission. There are also codes Z85.6, Personal history of leukaemia, and Z85.79, Personal history of other malignant neoplasms of lymphoid, haematopoietic and related tissues. If the documentation is unclear as to whether the leukaemia has achieved remission, the provider should be queried.
See Section I.C.21. Factors influencing health status and contact with health services, History (of)
o. Aftercare Following Surgery for Neoplasm
See Section I.C.21. Factors influencing health status and contact with health services, Aftercare
p. Follow-up Care for Completed Treatment of a Malignancy
See Section I.C.21. Factors influencing health status and contact with health services, Follow-up
q. Prophylactic Organ Removal for Prevention of Malignancy
See Section I.C. 21, Factors influencing health status and contact with health services, Prophylactic organ removal
r. Malignant Neoplasm Associated with Transplanted Organ
A malignant neoplasm of a transplanted organ should be coded as a transplant complication. Assign first the appropriate code from category T86.-, ICD-10-CM Official Guidelines for Coding and Reporting FY 2026 Page 39 of 121 Complications of transplanted organs and tissue, followed by code C80.2, Malignant neoplasm associated with transplanted organ. Use an additional code for the specific malignancy.
s. Breast Implant Associated Anaplastic Large Cell Lymphoma
Breast implant associated anaplastic large cell lymphoma (BIA-ALCL) is a type of lymphoma that can develop around breast implants. Assign code C84.7A, Anaplastic large cell lymphoma, ALK-negative, breast, for BIA-ALCL or C84.7B, Anaplastic large cell lymphoma, ALK-negative, in remission, for BIAALCL in remission. Do not assign a complication code from chapter 19.
t. Secondary Malignant Neoplasm of Lymphoid Tissue
When a malignant neoplasm of lymphoid tissue metastasises beyond the lymph nodes, a code from categories C81-C85 with a final character identifying "extranodal and solid organ sites" should be assigned rather than a code for the secondary neoplasm of the affected solid organ. For example, for metastasis of diffuse large B-cell lymphoma to the lung, brain and left adrenal gland, assign code C83.398, Diffuse large B-cell lymphoma of other extranodal and solid organ sites.
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Practice Scenarios
5 Scenario Examples for ICD-10-CM Chapter 2 Guidelines
1
Scenario 1: Primary Lung Cancer with Liver Metastasis
Clinical Situation: A patient is admitted for chemotherapy to treat primary lung cancer that has metastasised to the liver. The chemotherapy is the chief reason for admission.
Correct Coding Sequence:
  1. Z51.11 - Encounter for antineoplastic chemotherapy (Principal diagnosis)
  1. C34.90 - Malignant neoplasm of unspecified part of bronchus or lung (Secondary diagnosis)
  1. C78.7 - Secondary malignant neoplasm of liver and intrahepatic bile duct (Additional diagnosis)
Guideline Applied: Guideline 6 - When admission is chiefly for chemotherapy, assign Z51.11 first, followed by the malignancy codes.
2
Scenario 2: Anaemia Due to Colon Cancer
Clinical Situation: A patient with colon cancer is admitted solely for treatment of severe anaemia related to the malignancy. The patient receives blood transfusion.
Correct Coding Sequence:
  1. C18.9 - Malignant neoplasm of colon, unspecified (Principal diagnosis)
  1. D63.0 - Anaemia in neoplastic disease (Secondary diagnosis)
Guideline Applied: Guideline 1 - For anaemia associated with malignancy, sequence the malignancy first, then D63.0.
3
Scenario 3: Dehydration from Radiation Therapy
Clinical Situation: A patient undergoing radiation therapy for breast cancer develops severe dehydration and is admitted for IV rehydration only.
Correct Coding Sequence:
  1. E86.0 - Dehydration (Principal diagnosis)
  1. C50.919 - Malignant neoplasm of unspecified site of unspecified female breast (Secondary diagnosis)
  1. Y84.2 - Radiological procedure and radiotherapy as the cause of abnormal reaction (Additional diagnosis)
Guideline Applied: Guideline 2 - For complications from radiotherapy, sequence the complication first, followed by the neoplasm and Y84.2.
4
Scenario 4: Treatment of Brain Metastasis from Breast Cancer
Clinical Situation: A patient with a history of breast cancer (previously excised, no current treatment to breast) is admitted for surgical removal of a brain metastasis. Treatment is directed only at the brain metastasis.
Correct Coding Sequence:
  1. C79.31 - Secondary malignant neoplasm of brain (Principal diagnosis)
  1. Z85.3 - Personal history of malignant neoplasm of breast (Secondary diagnosis)
Guideline Applied: Guidelines 9 and d - When treatment is directed toward the secondary site only, the metastatic site is principal diagnosis. Use Z85 code for the previously excised primary site.
5
Scenario 5: Pathological Fracture from Bone Metastasis
Clinical Situation: A patient with prostate cancer develops a pathological fracture of the femur due to bone metastasis. The patient is admitted for orthopaedic treatment of the fracture.
Correct Coding Sequence:
  1. M84.551A - Pathological fracture in neoplastic disease, right femur, initial encounter (Principal diagnosis)
  1. C79.51 - Secondary malignant neoplasm of bone (Secondary diagnosis)
  1. C61 - Malignant neoplasm of prostate (Additional diagnosis)
Guideline Applied: Guideline 13 - When the focus of treatment is the fracture, sequence M84.5 first, followed by the neoplasm codes.
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