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C50.321 ICD-10-CM Code: Malignant neoplasm of lower-inner quadrant of right male breast

C50.321 maps to CMS-HCC V28 23. A source-labeled RAF reference is available. Documentation must support MEAT. MEAT criteria · RAF Calculator · HCC coding software

ICD-10-CM Code View

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FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of breast (C50)

C50.321

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

Malignant neoplasm of lower-inner quadrant of right male breast

Cancer that starts in the lower-inner area of the right breast in a male patient.

Buddy the Bee presenting code insight

Buddy Insight

Malignant neoplasm of the lower-inner quadrant of right male breast represents invasive breast cancer requiring staging, treatment planning, and ongoing surveillance.

CMS-HCC V28

HCC 23

Code-level coefficient reference

CMS-HCC V24

Historical

Historical

Not used for CY2026 payment

ACA/HHS

N/A

—

Not mapped

ESRD/PACE

N/A

—

Not mapped

RXHCC

HCC 22

Code-level coefficient reference

Code Book Path

Official
C50.3Malignant neoplasm of lower-inner quadrant of breast
C50.32Malignant neoplasm of lower-inner quadrant of breast, male
C50.321Malignant neoplasm of lower-inner quadrant of right male breast

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for C50.321 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C50.321 in this effective period.

Related Child Codes

Official
C50.322Malignant neoplasm of lower-inner quadrant of left male breast
C50.329Malignant neoplasm of lower-inner quadrant of unspecified male breast

Includes

Official

ICD-10-CM does not list Includes notes for C50.321 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for C50.321 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C50.321 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C50.321 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C50.321 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance
Pathologic confirmation of invasive malignancy (biopsy with histologic type — ductal, lobular, etc.)
Laterality: right breast
Gender documented as male to support gender-specific code selection
Quadrant or subsite location: lower-inner quadrant

MEAT Support

HCC Buddy guidance
Pathologic confirmation of invasive malignancy (biopsy with histologic type — ductal, lobular, etc.)
Laterality: right breast
Gender documented as male to support gender-specific code selection
Quadrant or subsite location: lower-inner quadrant

Audit Caution

HCC Buddy guidance
Selecting female breast codes (C50.31x) instead of male codes (C50.32x)
Confusing quadrant positions — lower-inner is below the nipple toward the sternum
Male breast cancer in the lower-inner quadrant is exceptionally rare; ensure pathologic confirmation
Selecting wrong laterality — verify right side from documentation

Common Mistakes

HCC Buddy guidance
C50.322 — Lower-inner quadrant of left male breast; verify laterality
C50.329 — Lower-inner quadrant unspecified male; use only when laterality unknown
C50.311 — Same laterality but female breast; verify patient gender
C50.221-C50.229 — Upper-inner quadrant of male breast; same medial orientation, different vertical position

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 C50.321 an HCC code?

Yes. C50.321 (Malignant neoplasm of lower-inner quadrant of right male breast) maps to HCC 23, Prostate, Breast, and Other Cancers and Tumors under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.186. 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: C50.321 is billable and maps to V28 HCC 23, Prostate, Breast, and Other Cancers and Tumors. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code
C50.321
Description
Malignant neoplasm of lower-inner quadrant of right male breast
HCC (V28)
HCC 23 — Prostate, Breast, and Other Cancers and Tumors
RAF reference coefficient
0.186
Billable
Yes
Payment year
2026

HCC Category Mapping

V28HCC 23, Prostate, Breast, and Other Cancers and Tumors
0.186
RxHCCHCC 22, Prostate, Breast, Bladder, and Other Cancers and Tumors
Not separately weighted

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 C50.321 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT Criteria for C50.321

For C50.321 to 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 C50.321 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

C50.321 is the ICD-10-CM diagnosis code for malignant neoplasm of lower-inner quadrant of right male breast. Cancer that starts in the lower-inner area of the right breast in a male patient. C50.321 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of breast (c50).

Under the CMS-HCC V28 risk adjustment model, C50.321 maps to Prostate, Breast, and Other Cancers and Tumors (HCC 23) with a source-labeled community, non-dual, aged reference coefficient of 0.186. No V24 mapping is shown for C50.321; use the applicable model and payment year when reviewing the V28 mapping. 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. 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 both the quadrant location (lower-inner) and laterality (right) are clearly documented. Because C50.321 maps to an HCC category, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) before the diagnosis is used for risk adjustment. 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 C50.321 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •Verify both the quadrant location (lower-inner) and laterality (right) are clearly documented
  • •Male breast cancer in the lower-inner quadrant is rare; ensure documentation accuracy

Clinical Significance

Malignant neoplasm of the lower-inner quadrant of right male breast represents invasive breast cancer requiring staging, treatment planning, and ongoing surveillance. Breast cancer is risk-adjusted because it demands significant healthcare resources including surgery, radiation, chemotherapy, hormonal therapy, and long-term monitoring. Male breast cancer accounts for less than 1% of all breast cancers, making accurate gender-specific coding particularly important for tracking and research.

Documentation Requirements

  • ✓Pathologic confirmation of invasive malignancy (biopsy with histologic type — ductal, lobular, etc.)
  • ✓Laterality: right breast
  • ✓Gender documented as male to support gender-specific code selection
  • ✓Quadrant or subsite location: lower-inner quadrant
  • ✓Tumor size (T stage) and grade
  • ✓Lymph node status (N stage) — axillary, sentinel node biopsy results
  • ✓Estrogen receptor, progesterone receptor, and HER2 status
  • ✓Stage grouping (I-IV)
  • ✓Current treatment status (active treatment, hormonal therapy, surveillance)

Commonly Confused Codes

  • •C50.322: Lower-inner quadrant of left male breast; verify laterality
  • •C50.329: Lower-inner quadrant unspecified male; use only when laterality unknown
  • •C50.311: Same laterality but female breast; verify patient gender
  • •C50.221-C50.229: Upper-inner quadrant of male breast; same medial orientation, different vertical position
  • •C50.121-C50.129: Central portion of male breast; adjacent but distinct subsite
  • •N62: Gynecomastia; benign condition, not malignant

Child Codes

C50.321Malignant neoplasm of lower-inner quadrant of right male breast
HCC 22
C50.322Malignant neoplasm of lower-inner quadrant of left male breast
HCC 22
C50.329Malignant neoplasm of lower-inner quadrant of unspecified male breast
HCC 22

Code Hierarchy

└C50Malignant neoplasm of breast└C50.3Malignant neoplasm of lower-inner quadrant of breast└C50.32Malignant neoplasm of lower-inner quadrant of breast, male└C50.321Malignant neoplasm of lower-inner quadrant of right male breast
└C50.321Malignant neoplasm of lower-inner quadrant of right male breast

Because C50.321 maps to an HCC category, the documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) before the diagnosis is used for risk adjustment.

C50.321 maps to CMS-HCC V28 category 23, Prostate, Breast, and Other Cancers and Tumors. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. The mapping identifies a payment HCC category for C50.321. Review its source-labeled HCC coefficient above, check the RAF Calculator with complete member context for CMS-HCC V28 PY2026, and confirm the documentation the chart needs before the code is submitted. HCC Buddy shows no RAF score unless every required source and calculation check passes.

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