What is ICD-10 code C73?

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. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C73 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C73 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. C73 is a payment HCC under the CMS risk adjustment model. Under the CMS-HCC V28 risk adjustment model it maps to Prostate, Breast, and Other Cancers and Tumors with a community, non-dual, aged base RAF weight of 0.186. Under the older CMS-HCC V24 model it maps to Breast, Prostate, and Other Cancers and Tumors at RAF 0.150. V28 reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition. HCC Buddy maintains the V28 and V24 mapping, RAF weight, and MEAT documentation criteria for C73 sourced directly from the CMS-HCC model files.

Yes. C73 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. C73 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

What is the V28 vs V24 difference for C73?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. For C73, V28 maps to Prostate, Breast, and Other Cancers and Tumors at RAF 0.186 while V24 mapped to Breast, Prostate, and Other Cancers and Tumors at RAF 0.150. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting C73?

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 Because C73 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

C73: Malignant neoplasm of thyroid gland — ICD-10 | Prostate, Breast, and Other Cancers

ICD-10-CM Code View

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Code lookupC73Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of thyroid and other endocrine glands (C73-C75)

C73

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Malignant neoplasm of thyroid gland

Cancer that develops in the thyroid gland, a butterfly-shaped gland in the neck that produces hormones regulating metabolism.

Buddy Insight

Malignant neoplasm of the thyroid gland is one of the more common endocrine malignancies, with papillary thyroid carcinoma being the most prevalent subtype.

CMS-HCC V28

Mapped

HCC 23

Prostate, Breast, and Other C...

RAF 0.186

CMS-HCC V24

Mapped

HCC 12

Breast, Prostate, and Other C...

RAF 0.150

ACA/HHS

Mapped

HCC 13

HHS-HCC 13

Varies by metal level

ESRD/PACE

Mapped

HCC 12

Breast, Prostate, and Other C...

RAF 0.045

RXHCC

Mapped

HCC 22

Cancer, Other Specified Sites

RAF 0.124

Code Book Path

Official

C7Malignant neoplasms of thyroid and other endocrine glands (C73-C75)

C73Malignant neoplasm of thyroid gland

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for C73 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C73 in this effective period.

Related Child Codes

Official

ICD-10-CM does not list child codes under C73 for this display context.

Includes

Official

ICD-10-CM does not list Includes notes for C73 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for C73 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C73 in this effective period.

Use Additional

Official

code to identify any functional activity

Code Also

Official

ICD-10-CM does not list Code Also instructions for C73 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

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

MEAT Support

HCC Buddy guidance

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

Audit Caution

HCC Buddy guidance

Continuing to code C73 after treatment completion when the patient has no evidence of disease — should transition to Z85.850

Coding thyroid nodules or goiter as malignant without pathological confirmation

Not distinguishing between primary thyroid cancer and metastatic cancer involving the thyroid

Coding anaplastic thyroid carcinoma the same as well-differentiated types — while the ICD-10 code is the same, documentation should reflect the vastly different prognosis and treatment needs

Common Mistakes

HCC Buddy guidance

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

Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.

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

V28HCC 23, Prostate, Breast, and Other Cancers and Tumors

0.186

V24HCC 12, Breast, Prostate, and Other Cancers and Tumors

0.150

ESRDHCC 12, Breast, Prostate, and Other Cancers and Tumors

0.045

RxHCCHCC 22, Cancer, Other Specified Sites

0.124

Each model's RAF is its CMS base weight for that model's standard population, so 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 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.

Work C73 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

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.

Coder workflow notes

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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

Code Hierarchy

└C73Malignant neoplasm of thyroid gland

C73 ICD-10-CM Code: Malignant neoplasm of thyroid gland

HCC Buddy Code Card

C73

Is C73 an HCC code?

HCC Category Mapping

MEAT Criteria for C73

Get the V28 RAF + MEAT cheat sheet

What This Code Means

Coding Tips

Clinical Significance

Documentation Requirements

Use Additional Code

Commonly Confused Codes

Code Hierarchy

Work C73 in HCC Buddy