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C50.329 ICD-10-CM Code: Malignant neoplasm of lower-inner quadrant of unspecified male breast

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

C50.329

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

Malignant neoplasm of lower-inner quadrant of unspecified male breast

Cancer in the lower-inner area of a male breast when the specific side (right or left) is not specified.

Buddy the Bee presenting code insight

Buddy Insight

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

CMS-HCC V28

HCC 22

RAF 0.363

CMS-HCC V24

HCC 12

RAF 0.150

ACA/HHS

N/A

—

Not mapped

ESRD/PACE

HCC 12

RAF 0.045

RXHCC

HCC 22

RAF 0.124

Code Book Path

Official
C50.3Malignant neoplasm of lower-inner quadrant of breast
C50.32Malignant neoplasm of lower-inner quadrant of breast, male
C50.329Malignant neoplasm of lower-inner quadrant of unspecified male breast

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for C50.329 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C50.329 in this effective period.

Related Child Codes

Official
C50.321Malignant neoplasm of lower-inner quadrant of right male breast
C50.322Malignant neoplasm of lower-inner quadrant of left male breast

Includes

Official

ICD-10-CM does not list Includes notes for C50.329 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for C50.329 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C50.329 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C50.329 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C50.329 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance
Pathologic confirmation of invasive malignancy (biopsy with histologic type — ductal, lobular, etc.)
Laterality must be queried if not documented — right or left 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 must be queried if not documented — right or left 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
Not querying for laterality when using unspecified codes

Common Mistakes

HCC Buddy guidance
C50.321 — Right male; preferred when right documented
C50.322 — Left male; preferred when left documented
C50.319 — 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 C50.329 an HCC code?

Yes. C50.329 (Malignant neoplasm of lower-inner quadrant of unspecified male breast) maps to Bladder, Colorectal, and Other Cancers under the CMS-HCC V28 risk adjustment model (and Breast, Prostate, and Other Cancers and Tumors under V24), with a community non-dual aged RAF of 0.363. It is billable for payment year 2026.

Coder answer: C50.329 is billable and maps to V28 HCC 22, Bladder, Colorectal, and Other Cancers. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code
C50.329
Description
Malignant neoplasm of lower-inner quadrant of unspecified male breast
HCC (V28)
HCC 22 — Bladder, Colorectal, and Other Cancers
RAF
0.363
Billable
Yes
Payment year
2026

HCC Category Mapping

V28HCC 22, Bladder, Colorectal, and Other Cancers
0.363
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 C50.329 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for C50.329

For C50.329 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 C50.329 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

C50.329 is the ICD-10-CM diagnosis code for malignant neoplasm of lower-inner quadrant of unspecified male breast. Cancer in the lower-inner area of a male breast when the specific side (right or left) is not specified. C50.329 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, C50.329 maps to Bladder, Colorectal, and Other Cancers (HCC 22) with a community, non-dual, aged base RAF weight of 0.363. Under the older CMS-HCC V24 model, C50.329 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.

Query the provider for laterality information when possible, as unspecified codes are less preferred. Because C50.329 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 C50.329 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •Query the provider for laterality information when possible, as unspecified codes are less preferred
  • •This code should only be used when laterality cannot be determined from available documentation

Clinical Significance

Malignant neoplasm of the lower-inner quadrant of unspecified 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. The unspecified laterality indicates documentation does not identify the affected side, which should trigger a provider query.

Documentation Requirements

  • ✓Pathologic confirmation of invasive malignancy (biopsy with histologic type — ductal, lobular, etc.)
  • ✓Laterality must be queried if not documented — right or left 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

  • •C50.321: Right male; preferred when right documented
  • •C50.322: Left male; preferred when left documented
  • •C50.319: 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└C50.329Malignant neoplasm of lower-inner quadrant of unspecified male breast
└C50.329Malignant neoplasm of lower-inner quadrant of unspecified male breast

Because C50.329 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.

C50.329 maps to CMS-HCC V28 category 22, Bladder, Colorectal, and Other Cancers. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. Because C50.329 carries a payment HCC, you can see what it adds to a RAF score and check the documentation the chart needs before it is submitted.

More on C50.329

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