C73
BillableMalignant neoplasm of thyroid gland
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C73 an HCC code?
Yes. C73 maps to Prostate, Breast, and Other Cancers and Tumors under the CMS-HCC V28 risk adjustment model (and Breast, Prostate, and Other Cancers and Tumors under V24).
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.
MEAT Criteria for C73
For C73to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically — it has to be re-documented and supported each calendar year.
- 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
Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed C73 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C73 is the ICD-10-CM diagnosis code for malignant neoplasm of thyroid gland. Cancer that develops in the thyroid gland, a butterfly-shaped gland in the neck that produces hormones regulating metabolism. C73 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of thyroid and other endocrine glands (c73-c75).
Under the CMS-HCC V28 risk adjustment model, C73 maps to Prostate, Breast, and Other Cancers and Tumors (HCC 23) with a community, non-dual, aged base RAF weight of 0.186. Under the older CMS-HCC V24 model, C73 maps to Breast, Prostate, and Other Cancers and Tumors (HCC 12) with a community, non-dual, aged base RAF weight of 0.150. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.
This code does not differentiate between histological types (papillary, follicular, medullary, anaplastic); review pathology reports for histology if needed for treatment planning. Because C73 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. 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, RAF weights, and MEAT documentation criteria for C73 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This code does not differentiate between histological types (papillary, follicular, medullary, anaplastic); review pathology reports for histology if needed for treatment planning
- •Ensure documentation specifies thyroid gland involvement and not metastatic disease to the thyroid from another primary site
Clinical Significance
Malignant neoplasm of the thyroid gland is one of the more common endocrine malignancies, with papillary thyroid carcinoma being the most prevalent subtype. Despite generally favorable prognosis for well-differentiated types, this diagnosis carries meaningful risk adjustment weight and requires lifelong surveillance with thyroid function monitoring and cancer recurrence screening. Accurate coding distinguishes active malignancy from personal history of thyroid cancer.
Documentation Requirements
- ✓Pathology report confirming malignancy with histological type (papillary, follicular, medullary, anaplastic, or poorly differentiated)
- ✓Current status — active disease vs. in remission vs. history of (Z85.850 for personal history)
- ✓Staging information (TNM staging) when available
- ✓Treatment status — post-thyroidectomy, radioactive iodine therapy, current surveillance
- ✓Thyroglobulin levels and thyroid function tests supporting ongoing monitoring
Use Additional Code
- code to identify any functional activity
Commonly Confused Codes
- •Z85.850 — Personal history of malignant neoplasm of thyroid: Use when cancer is resolved/in remission with no evidence of disease, not during active treatment
- •D34 — Benign neoplasm of thyroid gland: Thyroid adenomas and benign nodules are not malignant
- •E04.1 — Nontoxic single thyroid nodule: Thyroid nodules are not automatically malignant
- •D44.0 — Neoplasm of uncertain behavior of thyroid gland: Use when malignancy is not yet confirmed
- •C79.89 — Secondary malignant neoplasm of other specified sites: Metastatic cancer TO the thyroid from another primary