C78.02
BillableSecondary malignant neoplasm of left lung
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C78.02 an HCC code?
Yes. C78.02 maps to Metastatic Cancer and Acute Leukemia under the CMS-HCC V28 risk adjustment model (and Metastatic Cancer and Acute Leukemia 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 C78.02
For C78.02 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 C78.02 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C78.02 is the ICD-10-CM diagnosis code for secondary malignant neoplasm of left lung. Cancer that has spread to the tissue of the left lung from a cancer that originated elsewhere in the body. C78.02 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of ill-defined, other secondary and unspecified sites (c76-c80).
Under the CMS-HCC V28 risk adjustment model, C78.02 maps to Metastatic Cancer and Acute Leukemia (HCC 17) with a community, non-dual, aged base RAF weight of 0.368. Under the older V24 model, C78.02 mapped to the same category but with a base RAF weight of 2.484 — V28 recalibrated weights across the entire model. 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 is specific to left lung involvement; verify laterality in documentation before assigning this code. Because C78.02 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 C78.02 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This code is specific to left lung involvement; verify laterality in documentation before assigning this code
- •Always identify and code the primary cancer site separately when known
Clinical Significance
Secondary malignant neoplasm of the left lung confirms metastatic cancer with documented laterality. Left lung metastases carry the same clinical significance as right-sided involvement but require laterality documentation for accurate coding. Proper laterality capture demonstrates quality documentation and supports precise treatment planning.
Documentation Requirements
- ✓Primary cancer site must be documented and coded separately
- ✓Explicit documentation of left lung involvement — 'left lung metastasis' or equivalent
- ✓Imaging or pathological confirmation of metastatic disease
- ✓Number and distribution of metastatic lesions
- ✓Treatment plan or status — surgical candidacy, systemic therapy, or palliation
Commonly Confused Codes
- •C34.12 — Primary malignant neoplasm of upper lobe, left bronchus or lung; primary versus secondary distinction is critical
- •C78.00 — Secondary malignant neoplasm of unspecified lung; always specify laterality when documented
- •C78.01 — Secondary malignant neoplasm of right lung; verify laterality from imaging reports
- •C78.2 — Secondary malignant neoplasm of pleura; left pleural disease requires a different code