2027 ICD-10-CM Diagnosis Code C78.00Secondary malignant neoplasm of unspecified lung
ICD-10-CM Codes›C00–D49›C76-C80›C78
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Risk Adjusts — HCC 17
- Chronic Condition
C78.00 is a billable ICD-10-CM diagnosis code for secondary malignant neoplasm of unspecified lung. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 180 through 182. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 26 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Secondary malignancies.
For Medicare Advantage risk adjustment, C78.00 maps to CMS-HCC Category 17 (Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic) under the V28 model, adding a risk factor of about 4.209 for a community, non-dual, aged beneficiary in payment year 2027.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
C78.00 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2027.
Source: CMS Payment Year 2027 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Hilar mass
- Main bronchus involved by direct extension of malignant neoplasm
- Malignant neoplasm of carina of trachea
- Metastatic carcinoma to lower lobe of lung
- Metastatic carcinoma to main bronchus
- Metastatic giant cell carcinoma to lung
- Metastatic large cell carcinoma to lung
- Metastatic malignant neoplasm to bronchus
- Metastatic malignant neoplasm to carina
- Metastatic malignant neoplasm to hilus of lung
- Metastatic malignant neoplasm to lung
- Metastatic malignant neoplasm to main bronchus
- Metastatic malignant neoplasm to trachea
- Metastatic non-small cell lung cancer
- Metastatic squamous cell carcinoma to bronchus
- Metastatic squamous cell carcinoma to lung
- Metastatic undifferentiated large cell carcinoma to lung
- Metastatic well-differentiated neuroendocrine tumor
- Metastatic well-differentiated neuroendocrine tumor to lung
- Neoplasm of carina
- Neoplasm of hilus of lung
- Neoplasm of lower respiratory tract and mediastinum
- Tumor invasion into lung parenchyma
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to C78.00: its own notes plus those printed at C78 and Chapter 2. A note printed at a category, block or chapter applies to every code under it.
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
Notes
General instructions on how these codes are used.
- Functional activity
- All neoplasms are classified in this chapter, whether they are functionally active or not. An additional code from Chapter 4 may be used, to identify functional activity associated with any neoplasm.
- Morphology [Histology]
- Chapter 2 classifies neoplasms primarily by site (topography), with broad groupings for behavior, malignant, in situ, benign, etc. The Table of Neoplasms should be used to identify the correct topography code. In a few cases, such as for malignant melanoma and certain neuroendocrine tumors, the morphology (histologic type) is included in the category and codes.
- Primary malignant neoplasms overlapping site boundaries
- A primary malignant neoplasm that overlaps two or more contiguous (next to each other) sites should be classified to the subcategory/code .8 ('overlapping lesion'), unless the combination is specifically indexed elsewhere. For multiple neoplasms of the same site that are not contiguous, such as tumors in different quadrants of the same breast, codes for each site should be assigned.
- Malignant neoplasm of ectopic tissue
- Malignant neoplasms of ectopic tissue are to be coded to the site mentioned, e.g., ectopic pancreatic malignant neoplasms are coded to pancreas, unspecified (C25.9).
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name C78.00, its category, or a range that includes it.
Applicable To 2
These notes mention C78.00.
Code First 1
These codes say to code first a condition named in the note, and C78.00 is one of the conditions named.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Metastatic Malignant Neoplasm to the Lung
the spread of a malignant neoplasm to the lung. this may be from a primary lung malignant neoplasm, or from a malignant neoplasm at a distant site.
Table of NeoplasmsClinical
Anatomical sites in the Table of Neoplasms that reference this code family.
| Site | Malig. Primary | Malig. Secondary | Ca in situ | Benign | Uncertain | Unspec. |
|---|---|---|---|---|---|---|
| bronchiogenic, bronchogenic (lung) | C34.9 | C78.0 | D02.2 | D14.3 | D38.1 | D49.1 |
| bronchiole | C34.9 | C78.0 | D02.2 | D14.3 | D38.1 | D49.1 |
| bronchus | C34.9 | C78.0 | D02.2 | D14.3 | D38.1 | D49.1 |
| bronchus › carina | C34.0 | C78.0 | D02.2 | D14.3 | D38.1 | D49.1 |
| bronchus › lower lobe of lung | C34.3 | C78.0 | D02.2 | D14.3 | D38.1 | D49.1 |
| bronchus › main | C34.0 | C78.0 | D02.2 | D14.3 | D38.1 | D49.1 |
| bronchus › middle lobe of lung | C34.2 | C78.0 | D02.21 | D14.31 | D38.1 | D49.1 |
| bronchus › upper lobe of lung | C34.1 | C78.0 | D02.2 | D14.3 | D38.1 | D49.1 |
| carina (bronchus) | C34.0 | C78.0 | D02.2 | D14.3 | D38.1 | D49.1 |
| hilus of lung | C34.0 | C78.0 | D02.2 | D14.3 | D38.1 | D49.1 |
| lingula, lung | C34.1 | C78.0 | D02.2 | D14.3 | D38.1 | D49.1 |
| lung | C34.9 | C78.0 | D02.2 | D14.3 | D38.1 | D49.1 |
| lung › azygos lobe | C34.1 | C78.0 | D02.2 | D14.3 | D38.1 | D49.1 |
| lung › carina | C34.0 | C78.0 | D02.2 | D14.3 | D38.1 | D49.1 |
| lung › hilus | C34.0 | C78.0 | D02.2 | D14.3 | D38.1 | D49.1 |
| lung › lingula | C34.1 | C78.0 | D02.2 | D14.3 | D38.1 | D49.1 |
| lung › lobe NEC | C34.9 | C78.0 | D02.2 | D14.3 | D38.1 | D49.1 |
| lung › lower lobe | C34.3 | C78.0 | D02.2 | D14.3 | D38.1 | D49.1 |
| lung › main bronchus | C34.0 | C78.0 | D02.2 | D14.3 | D38.1 | D49.1 |
| lung › middle lobe | C34.2 | C78.0 | D02.21 | D14.31 | D38.1 | D49.1 |
| lung › upper lobe | C34.1 | C78.0 | D02.2 | D14.3 | D38.1 | D49.1 |
| pulmonary [See Also: Neoplasm, lung] | C34.9 | C78.0 | D02.2 | D14.3 | D38.1 | D49.1 |
| subpleural | C34.9 | C78.0 | D02.2 | D14.3 | D38.1 | D49.1 |
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Convert C78.00 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About C78.00Overview
What is the ICD-10 code for secondary malignant neoplasm of unspecified lung?
The ICD-10-CM code for secondary malignant neoplasm of unspecified lung is C78.00 (sometimes written as C7800). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is C78.00 (Secondary malignant neoplasm of lung) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report secondary malignant neoplasm of unspecified lung on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does C78.00 group to?
When secondary malignant neoplasm of unspecified lung is the principal diagnosis on an inpatient stay, it groups to MS-DRG 181, 180, 182, with relative weights from 0.7436 to 1.7800 depending on complications. Higher weights mean higher Medicare reimbursement.
Is C78.00 a CC or MCC?
CMS lists C78.00 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 26 closely related codes in its exclusion list.
Can C78.00 be reported with C7B.02?
Not as a rule. The Excludes1 note at C78, which applies to C78.00, lists "secondary carcinoid tumors of liver (C7B.02)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).
What HCC is C78.00?
C78.00 (secondary malignant neoplasm of unspecified lung) maps to CMS-HCC Category 17 (Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic), commonly written as HCC 17, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 8 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. In the Part D prescription drug model it maps to RxHCC 18.
Does C78.00 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, C78.00 adds a risk adjustment factor of about 4.209 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 1.952 to 4.235 depending on the payment segment). HCC 17 sits at the top of its hierarchy, so no other condition category supersedes it. See the full factor table on the HCC 17 category page.
