Alphabetic Index FY2027

C96.6

Unifocal Langerhans-cell histiocytosis

FY2027Chapter 2: Neoplasms/C81–C96 Malignant neoplasms of lymphoid, hematopoietic and related tissue

BillableComplete code, valid to report
Care settingsHome Health Primary · MMTA - Infectious Disease, Neoplasms, and Blood-Forming DiseasesHospital CC

C96.6 (also written C966) is a billable ICD-10-CM diagnosis code for unifocal Langerhans-cell histiocytosis. It is part of the FY2027 code set, effective October 1, 2026. It is one of the 11 codes in category C96 (Other and unspecified malignant neoplasms of lymphoid, hematopoietic and related tissue). The Alphabetic Index lists it under 12 entries. Its coding notes include 3 Excludes1 entries and 4 Excludes2 entries.

Excludes1

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

This code
  • multifocal and multisysemic (disseminated) Langerhans-cell histiocytosis (C96.0)
  • multifocal and unisystemic Langerhans-cell histiocytosis (C96.5)
Inherited from C96 Other and unspecified malignant neoplasms of lymphoid, hematopoietic and related tissue
  • personal history of other malignant neoplasms of lymphoid, hematopoietic and related tissues (Z85.79)

Excludes2

Not included here. Both codes may be reported if the patient has both conditions.

Also from chapter/block level (4 notes)
Inherited from C81–C96 Malignant neoplasms of lymphoid, hematopoietic and related tissue
  • Kaposi's sarcoma of lymph nodes (C46.3)
  • secondary and unspecified neoplasm of lymph nodes (C77.-)
  • secondary neoplasm of bone marrow (C79.52)
  • secondary neoplasm of spleen (C78.89)

Care settings

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

Home Health Primary

Accepted as the primary (principal) diagnosis on a home health claim. The Home Health Grouper assigns it to the MMTA - Infectious Disease, Neoplasms, and Blood-Forming Diseases clinical group.

Source: CMS Home Health Grouper Software v07.2.26, effective October 1, 2026

Hospital CC

Counts as a complication or comorbidity (CC) when reported as a secondary diagnosis on an inpatient claim. It does not count when the principal diagnosis is one of the 41 codes in its exclusion list. Some MS-DRGs also ignore a CC or MCC that defines the DRG.

Source: CMS MS-DRG Definitions Manual v44, effective October 1, 2026, Appendix C

Inclusion terms

Conditions classified to this code.

This code
  • Eosinophilic granuloma
  • Histiocytosis X, unifocal
  • Histiocytosis X NOS
  • Langerhans-cell histiocytosis NOS

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. 12 entries