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.

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.

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.

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.

Coding and sequencing of complications associated with the malignancies or with the therapy thereof are subject to the following guidelines:

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

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.

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.

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.

See Section I.C.6. for information on coding admission/encounter for pain control/management.

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.

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.

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

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.

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.

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

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)

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)

See Section I.C.21. Factors influencing health status and contact with health services, Aftercare

See Section I.C.21. Factors influencing health status and contact with health services, Follow-up

See Section I.C. 21, Factors influencing health status and contact with health services, Prophylactic organ removal

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.

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.

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.