Excludes1 pair
C79.9 vs C80.0
C79.9 and C80.0 are not coded together. ICD-10-CM declares them mutually exclusive with an Excludes1 note — the two conditions are not expected to occur together, so exactly one of them is normally correct for a given encounter. The Official Guidelines carve out one exception: if the two conditions are clearly unrelated to each other, both may be reported.
The official note, declared on C79.9
carcinomatosis NOS (C80.0)
C79.9
Secondary malignant neoplasm of unspecified site
BillableUnspecified
- Chapter 2
- Neoplasms
- Section
- C76-C80
Use when the record says
- Metastatic cancer NOS
- Metastatic disease NOS
Indexed under
- Disease, diseased › metastatic
- Metastasis, metastatic › disease
C80.0
Disseminated malignant neoplasm, unspecified
BillableUnspecified
- Chapter 2
- Neoplasms
- Section
- C76-C80
Use when the record says
- Carcinomatosis NOS
- Generalized cancer, unspecified site (primary) (secondary)
- Generalized malignancy, unspecified site (primary) (secondary)
Indexed under
- Carcinomatosis
- Carcinoma › generalized, with unspecified primary site
- Carcinomatosis › unspecified site (primary) (secondary)
Excludes1 is not always absolute: where two conditions covered by the note are genuinely unrelated, CMS guidance permits reporting both. Document the reasoning rather than assuming it. More on Excludes1 vs Excludes2 · FY2027