Alphabetic Index FY2027

C80.1

Malignant (primary) neoplasm, unspecified

FY2027Chapter 2: Neoplasms/C76–C80 Malignant neoplasms of ill-defined, other secondary and unspecified sites

BillableComplete code, valid to report
Care settingsIPF Comorbidity · Oncology Treatment

C80.1 (also written C801) is a billable ICD-10-CM diagnosis code for malignant (primary) neoplasm, unspecified. It is part of the FY2027 code set, effective October 1, 2026. It is one of the 3 codes in category C80 (Malignant neoplasm without specification of site). The Alphabetic Index lists it under 11 entries. Its coding notes include 3 Excludes1 entries.

Guidelines tip

From the FY2027 Official Guidelines. ICD10Ref adds no rules of its own.

C80.0 is not a substitute for coding the primary site and every known secondary site. C80.1 is used only when the primary site cannot be determined.

Guidelines I.C.2.j; I.C.2.kDisseminated and unspecified malignant neoplasmRead the official text

Excludes1

Not coded here. The listed conditions generally should not be reported together.

This code
  • secondary malignant neoplasm of unspecified site (C79.9)
Inherited from C80 Malignant neoplasm without specification of site
  • malignant carcinoid tumor of unspecified site (C7A.00)
  • malignant neoplasm of specified multiple sites- code to each site

Care settings

How CMS programs treat this code. These are CMS claim edits and list entries, not coverage or eligibility rules.

IPF Comorbidity

On the CMS IPF comorbidity list.

Comorbidity categoryFactor
Oncology Treatment1.44
It counts as a comorbidity when reported as a secondary diagnosis and actively treated during the stay. An IPF receives only one adjustment within a category and can receive adjustments in more than one category.

Source: CMS IPF PPS FY 2027 final rule (CMS-1847-F), Addendum B-3 (comorbidity codes with adjustment factor); effective for discharges on or after October 1, 2026

Inclusion terms

Conditions classified to this code.

This code
  • Cancer NOS
  • Cancer unspecified site (primary)
  • Carcinoma unspecified site (primary)
  • Malignancy unspecified site (primary)

Notes

Also from chapter/block level (8 notes)
Inherited from Chapter 2 Neoplasms
  • Functional activity
  • All neoplasms are classified in this chapter, whether they are functionally active or not. An additional code from Chapter 4 may be used, to identify functional activity associated with any neoplasm.
  • Morphology [Histology]
  • Chapter 2 classifies neoplasms primarily by site (topography), with broad groupings for behavior, malignant, in situ, benign, etc. The Table of Neoplasms should be used to identify the correct topography code. In a few cases, such as for malignant melanoma and certain neuroendocrine tumors, the morphology (histologic type) is included in the category and codes.
  • 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 tumors 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 mentioned, e.g., ectopic pancreatic malignant neoplasms are coded to pancreas, unspecified (C25.9).

Alphabetic Index terms

Terms the official Alphabetic Index lists for this code. 11 entries