C85.29 ICD-10-CM Code: Mediastinal (thymic) large B-cell lymphoma, extranodal and solid organ sites
C85.29 maps to CMS-HCC V28 21. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · free HCC coding tools
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FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of lymphoid, hematopoietic and related tissue (C81-C96)
C85.29
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceMediastinal (thymic) large B-cell lymphoma, extranodal and solid organ sites
This is a type of aggressive blood cancer (lymphoma) that starts in the thymus gland in the chest and has spread to organs outside the lymph node system. It is a fast-growing cancer made up of large B-cells.
Buddy Insight
Mediastinal (thymic) large B-cell lymphoma involving extranodal and solid organ sites indicates disease that has spread beyond the primary mediastinal origin.
CMS-HCC V28
MappedHCC 21
Coefficient HCC 21: 0.671 (Community Non-Dual Aged (CNA))
CMS-HCC V24
HistoricalHistorical
Not used for CY2026 payment
ACA/HHS
MappedHCC 010
Code-level coefficient reference
ESRD/PACE
MappedHCC 10
Code-level coefficient reference
RXHCC
MappedHCC 21
Code-level coefficient reference
Code Book Path
Inclusion Terms
OfficialNo inclusion terms are included in this display for C85.29. Check the code and parent instructions in the Code Book.
Excludes 2
Official- Kaposi's sarcoma of lymph nodes (C46.3)Inherited from C81-C96
- secondary and unspecified neoplasm of lymph nodes (C77.-)Inherited from C81-C96
- secondary neoplasm of bone marrow (C79.52)Inherited from C81-C96
- secondary neoplasm of spleen (C78.89)Inherited from C81-C96
Related Codes
Includes
OfficialNo Includes notes are included in this display for C85.29. Check the code and parent instructions in the Code Book.
Excludes 1
Official- other specified types of T/NK-cell lymphoma (C86.-)Inherited from C85
- personal history of non-Hodgkin lymphoma (Z85.72)Inherited from C85
Code First
OfficialNo Code First sequencing instructions are included in this display for C85.29. Check the code and parent instructions in the Code Book.
Use Additional
OfficialNo Use Additional Code instructions are included in this display for C85.29. Check the code and parent instructions in the Code Book.
Code Also
OfficialNo Code Also instructions are included in this display for C85.29. Check the code and parent instructions in the Code Book.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →
Is C85.29 an HCC code?
Yes. C85.29 (Mediastinal (thymic) large B-cell lymphoma, extranodal and solid organ sites) maps to HCC 21, Lymphoma and Other Cancers under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.671. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.
Coder answer: C85.29 is billable and maps to V28 HCC 21, Lymphoma and Other Cancers. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.
- Code
- C85.29
- Description
- Mediastinal (thymic) large B-cell lymphoma, extranodal and solid organ sites
- HCC (V28)
- HCC 21 — Lymphoma and Other Cancers
- RAF reference coefficient
- 0.671
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. Weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.
Work C85.29 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →
MEAT review for C85.29
For C85.29, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.
- MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
- EEvaluate: test results, medication response, or physical findings reviewed by the provider
- AAssess: explicit mention in the assessment or plan with acknowledgment of status
- TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis
Coder workflow notes
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What This Code Means
C85.29 is the ICD-10-CM diagnosis code for mediastinal (thymic) large b-cell lymphoma, extranodal and solid organ sites. This is a type of aggressive blood cancer (lymphoma) that starts in the thymus gland in the chest and has spread to organs outside the lymph node system. It is a fast-growing cancer made up of large B-cells. C85.29 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of lymphoid, hematopoietic and related tissue (c81-c96).
Under the CMS-HCC V28 risk adjustment model, C85.29 maps to Lymphoma and Other Cancers (HCC 21) with a source-labeled community, non-dual, aged reference coefficient of 0.671. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.
Verify documentation specifies both the mediastinal/thymic location AND extranodal/solid organ involvement before assigning this code, as the '29' indicates spread beyond lymph nodes. For C85.29, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.
HCC Buddy maintains structured V28 and V24 mapping, source-labeled coefficient references, and MEAT documentation criteria for C85.29 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Verify documentation specifies both the mediastinal/thymic location AND extranodal/solid organ involvement before assigning this code, as the '29' indicates spread beyond lymph nodes
- •Confirm the histology is documented as large B-cell lymphoma and review pathology reports to ensure accurate site of involvement for proper code selection
Clinical Significance
Mediastinal (thymic) large B-cell lymphoma involving extranodal and solid organ sites indicates disease that has spread beyond the primary mediastinal origin. This dissemination pattern affects prognosis and treatment approach, potentially requiring more aggressive regimens or radiation field modification. Extra-mediastinal spread occurs in a minority of cases and should be carefully documented for accurate staging.
Documentation Requirements
- ✓Original pathology confirming primary mediastinal (thymic) large B-cell lymphoma subtype with appropriate markers
- ✓Imaging or clinical confirmation of extranodal and solid organ sites involvement beyond the primary mediastinal mass
- ✓Documentation that this represents spread from primary mediastinal disease, not a de novo lymphoma at this site
- ✓Complete staging showing both primary mediastinal disease and secondary involvement
Commonly Confused Codes
- •C83.3x (Diffuse large B-cell lymphoma at same site): PMBCL spreading to extranodal and solid organ sites should still be coded as C85.2x, not as DLBCL
- •C85.1x (Unspecified B-cell lymphoma at same site): Use C85.2x when the mediastinal/thymic subtype is confirmed by pathology
- •C85.28 (PMBCL, lymph nodes of multiple sites): Use site-specific code when a single secondary site is involved; use C85.28 for multiple sites