ICD-10 Code C84.99 – Mature T/NK-cell lymphomas, unspecified, extranodal and solid organ sites (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C84.99 – Mature T/NK-cell lymphomas, unspecified, extranodal and solid organ sites
What it is
This code identifies a mature T-cell or NK-cell lymphoma with an unspecified subtype that involves extranodal tissue or a solid organ. Use it when the record confirms this lymphoma category but does not name a more specific site or histology.
Clinical signs
Clinical features vary; refer to documentation. Findings may reflect a lymphoma mass or organ involvement outside lymph nodes, with pathology confirming a mature T/NK-cell process.
When to use this code
Use C84.99 when the provider documents a mature T/NK-cell lymphoma, but the exact subtype is not stated and the disease is in an extranodal or solid organ site. Apply it when the note supports lymphoma involvement of a non-nodal organ and no more specific code is available. Check documentation if the site or histology is unclear.
Do not use for
Do not use this code for B-cell lymphomas, Hodgkin lymphoma, or leukemias. Avoid it when the record identifies a more specific T/NK-cell lymphoma subtype or a nodal-only disease site.
Coding tip
Query for the exact histology and site before assigning an unspecified code.