ICD-10 Codes for Lung Cancer: Complete Guide to Diagnosis and Billing
November 13, 2026
ICD-10 coding for lung cancer goes beyond identifying the patient as having cancer. The healthcare professional is supposed to find out the site where the tumor is found, ascertain the active state of the malignancy, and differentiate primary from metastatic cancer of the lungs.
Even a slight difference in documentation can cause an error in the diagnosis code, create problems with necessity determination, and increase payer review for the patient’s account.
Primary malignant lung neoplasms are coded under ICD-10-CM code category C34, but metastatic lung neoplasms and personal history of lung cancer have other ICD-10 codes.
In this post, we will look at the coding diagnosis codes, coding guidelines, and best practices for claim review.
What Is the ICD-10 Code for Lung Cancer?
Category C34 in the ICD-10-CM code set is used to identify malignant neoplasms of bronchus and lungs. There are several codes in category C34 which identify the affected lung, particular lobe, bronchus and overlap sites.
Some of them include:
C34.11: Malignant neoplasm of the upper lobe, right bronchus or lung.
C34.12: Malignant neoplasm of the upper lobe, left bronchus or lung.
C34.31: Malignant neoplasm of the lower lobe, right bronchus or lung.
C34.32: Malignant neoplasm of the lower lobe, left bronchus or lung.
C34.90: Malignant neoplasm of unspecified part of unspecified bronchus or lung.
The CMS ICD-10-CM code files provide the official reference for current diagnosis code selection.
Complete ICD-10 Code List for Lung Cancer
ICD-10-CM organizes primary lung malignancies by anatomical location. Accurate documentation helps coders identify the correct diagnosis without relying on unspecified codes unnecessarily.
| ICD-10 Code | Description |
| C34.00 | Malignant neoplasm of unspecified main bronchus |
| C34.01 | Malignant neoplasm of right main bronchus |
| C34.02 | Malignant neoplasm of left main bronchus |
| C34.10 | Malignant neoplasm of upper lobe, unspecified bronchus or lung |
| C34.11 | Malignant neoplasm of upper lobe, right bronchus or lung |
| C34.12 | Malignant neoplasm of upper lobe, left bronchus or lung |
| C34.2 | Malignant neoplasm of middle lobe, bronchus or lung |
| C34.30 | Malignant neoplasm of lower lobe, unspecified bronchus or lung |
| C34.31 | Malignant neoplasm of lower lobe, right bronchus or lung |
| C34.32 | Malignant neoplasm of lower lobe, left bronchus or lung |
| C34.80 | Malignant neoplasm of overlapping sites of unspecified bronchus and lung |
| C34.81 | Malignant neoplasm of overlapping sites of right bronchus and lung |
| C34.82 | Malignant neoplasm of overlapping sites of left bronchus and lung |
| C34.90 | Malignant neoplasm of unspecified part of unspecified bronchus or lung |
| C34.91 | Malignant neoplasm of unspecified part of right bronchus or lung |
| C34.92 | Malignant neoplasm of unspecified part of left bronchus or lung |
The codes are in line with the ICD-10-CM classification system. It is important for providers to go through the Tabular List and coding instructions before filing claims.
Why Anatomical Specificity Matters
For instance, consider a pathology report revealing the presence of adenocarcinoma in the right upper lung lobe.
The physician records the diagnosis and the site of the disease. The coder can code C34.11 rather than using the more non-specific code C34.91.
Nevertheless, when the clinical records mention just the right lung but do not indicate which lobe is affected, then C34.91 could actually be accurate.
Lung Cancer Coding: Why Providers Need Greater Accuracy
Lung cancer creates a substantial clinical and administrative workload for U.S. healthcare organizations.
According to the National Cancer Institute’s 2026 cancer estimates, the United States expects approximately:
- For instance, consider a pathology report revealing the presence of adenocarcinoma in the right upper lung lobe.
- The physician records the diagnosis and the site of the disease. The coder can code C34.11 rather than using the more non-specific code C34.91.
- Nevertheless, when the clinical records mention just the right lung but do not indicate which lobe is affected, then C34.91 could actually be accurate.
The CDC’s June 2026 lung cancer report also highlights the frequency of advanced-stage diagnoses.
For billing departments, the following are some coding problems that arise due to the complexity of cancer treatment. These include imaging, biopsies, surgery, chemotherapy, radiotherapy, and follow-up tests.
Each encounter requires diagnosis, selection and sequencing that reflect its actual purpose.
Primary vs. Metastatic Lung Cancer ICD-10 Codes
The main coding consideration includes deciding whether the origin of cancer is in the lungs or if it metastasized from somewhere else.
Primary Lung Cancer
Primary lung cancer develops from the bronchus or from the lung.
For instance, a patient is diagnosed with cancer in the left lower lobe of the lungs.
In that case, the proper code will be C34.32, provided that the malignancy belongs to C34.
Secondary or Metastatic Lung Cancer
Secondary lung cancer is defined by the development of malignancies that originate elsewhere and spread to the lungs.
The ICD-10-CM code for secondary lung cancer is C78.0.
| ICD-10 Code | Description |
| C78.00 | Secondary malignant neoplasm of unspecified lung |
| C78.01 | Secondary malignant neoplasm of right lung |
| C78.02 | Secondary malignant neoplasm of left lung |
Practical billing example:
A patient with colorectal cancer presents with proven metastasis to the right lung.
In this case, the coding department will assign C78.01 for the secondary cancer of the lung and other cancers that are appropriate from the encounter. Assigning a code for primary cancer of the lung in this case will be inaccurate.
The FY2027 ICD-10-CM Official Guidelines address diagnosis sequencing when treatment involves primary and secondary malignant sites.
History of Lung Cancer ICD-10 Code
A history of prior lung cancer does not necessarily mean there is an active malignancy that needs to be reported.
Z85.118 in the ICD-10-CM classification represents a personal history of other malignant neoplasms of the bronchus and lung.
This code is to be assigned if the patient had a prior malignancy coded in C34, which is currently absent from the body site and for which the patient no longer receives treatment.
When Should You Use Z85.118 Instead of C34?
Let us look at two scenarios.
Scenario 1: Treatment is ongoing
A patient has undergone lung cancer surgery and further radiation therapy to the primary site of cancer.
Malignancy code for the primary malignancy can be used since treatment of the malignancy is still ongoing.
Scenario 2: Treatment is finished
A patient is done with the treatment for primary lung cancer; there is no malignancy found on the original site and now comes back for follow-up.
Documentation supports Z85.118. In addition, for follow-up examination after completion of the treatment, coder need to consider Z08.
The official FY2027 coding guidelines explain how treatment status and evidence of existing disease determine the transition from active cancer coding to history coding.
Does Lung Cancer Type Affect ICD-10 Coding?
Non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC) are commonly distinguished from one another by healthcare providers.
They have their own characteristics, but in general, the ICD-10-CM coding system will code them based on their anatomical location under C34, and not specifically classify NSCLC or SCLC codes based on histology.
Examples of this include:
- NSCLC in the right upper lobe could justify C34.11.
- SCLC in the left lower lobe could justify C34.32.
It is important that the histology be noted for clinical and medical necessity purposes.
There are also instances when there can be an exception to the coding for neoplasms. One such exception is C7A.090 which refers to the malignant carcinoid tumor of the bronchus and lung.
The providers must determine if the pathology is truly malignant before coding a simple C34 code for all pulmonary malignancies.
Lung Cancer ICD-10 Coding Guidelines for Current Claims
The FY2027 ICD-10-CM code set applies to services from October 1, 2026, through September 30, 2027.
The CDC’s current ICD-10-CM release provides the official files.
1. Confirm the Reason for the Encounter
A patient’s history of cancer is not used as the principal diagnosis code for all visits.
For a visit that only addresses antineoplastic chemotherapy or immunotherapy, the guideline will instruct coders to use Z51.11 as the primary code.
For a visit that only involves antineoplastic radiation therapy, coders will use Z51.0 as the primary code.
Use the applicable malignancy diagnosis codes based on the sequencing guidelines.
2. Distinguish Confirmed and Suspected Diagnoses
Outpatient coders are not supposed to code an unconfirmed diagnosis of lung cancer as an established malignancy.
When the findings from imaging show a suspicious lesion in the lungs, but the provider has not confirmed it as malignancy, the coding must be done based on the findings or symptoms as per the outpatient guidelines.
The imaging findings do not confirm malignancy.
3. Identify Every Documented Malignant Site
Cancer may affect several anatomical areas for a patient.
Examine pathological results, oncology records, and recent clinical findings to determine the different malignancies that need to be reported.
Not every new cancer is necessarily metastatic; make sure of the relationship before categorizing them as such.
4. Follow Documentation and Sequencing Requirements
Anemia, dehydration, complications of therapy, or pain due to the neoplasm can all be linked to cancer encounters.
The correct initial or primary diagnosis code is contingent upon the circumstances surrounding the encounter and the appropriate coding rules.
What the treatment is aimed at doing needs to be taken into account rather than automatically coding C34 as the primary code.
Common Lung Cancer Coding Errors That Can Affect Claims
Cancer coding errors frequently begin with incomplete documentation or incorrect interpretation of treatment status.
| Coding error | Recommended action |
| Reporting C34.90 despite documented tumor location | Select the supported site-specific code |
| Confusing primary and metastatic cancer | Review pathology and provider assessment |
| Reporting active cancer after completed treatment | Confirm current disease and treatment status |
| Coding suspected outpatient cancer as confirmed | Follow outpatient diagnostic coding guidelines |
| Incorrect diagnosis sequencing | Review encounter purpose and official guidelines |
| Missing supporting medical necessity documentation | Reconcile clinical records and payer requirements |
Although an incorrect diagnosis does not necessarily mean denial, discrepancies may result in claim edits, medical necessity issues, documentation issues, and payment delays.
Healthcare providers can avoid discrepancies by performing thorough coding audits prior to claims submission.
How Can Providers Improve Lung Cancer Claim Accuracy?
A thorough pre-submission review will ensure that the clinical documentation provided by the provider corresponds to the diagnosis codes and services provided in the claim.
- Ensure proper diagnosis. Confirm the diagnosis of the treating provider, as well as the pathology results.
- Ensure correct anatomical site. Confirm the lung, the lobe and the main bronchus affected.
- Ensure proper malignancy. Distinguish between active malignancy, previous malignancy and metastasis.
- Confirm the purpose of the visit. Ensure whether the visit is related to evaluation, treatment, follow-up, or any other condition.
- Confirm any additional diagnoses. Confirm any metastases and complications.
- Ensure payer guidelines. Confirm the guidelines on coverage, authorizations and documentation of medical necessity.
- Lastly, confirm the claim. Review the diagnosis codes, clinical services, the providers’ information and new guidelines.
The structured [medical coding and claim review process] will assist oncology practices in finding any inconsistencies prior to submitting the claim to the payer.
Final Thoughts
For the proper coding of lung cancer using ICD-10 codes, there are three critical elements that must be considered: the location of the malignancy, the status of the cancer being active, and the reason for treatment.
ICD-10 code C34 is used when the primary lung malignancy occurs, C78.0 for the spread of cancer into the lungs, and Z85.118 when there is a personal history of specific primary lung malignancy.
When healthcare professionals properly record all of these elements, they will provide their coding team with a better foundation to select the right diagnosis codes.
It will also make the entire process more streamlined and efficient.
Frequently Asked Questions
1. Which ICD-10 code represents lung cancer?
ICD-10 category C34 represents malignant neoplasm of the bronchus and lung. The particular code varies based on the information regarding the tumor’s location and laterality.
2. Which ICD-10 code represents unspecified lung cancer?
C34.90 is used to indicate a malignant neoplasm of an unspecified part of an unspecified bronchus or lung. It should be used when there is not enough documentation to assign a more specific code.
3. Which ICD-10 code represents a history of lung cancer?
Z85.118 identifies a personal history of other malignant neoplasm of the bronchus and lung, which includes primary cancers coded under C34.
4. Which ICD-10 code is used for metastatic lung cancer?
Code C78.00 is used for secondary malignant neoplasm of unspecified lung; code C78.01 is used for the right lung; and code C78.02 is used for the left lung.
5. Are there different ICD-10 codes for small cell and non-small cell lung cancers?
In general, ICD-10-CM classifies these cancers as anatomically based primary lung cancers and does not include distinct C34 codes specifically for small cell or non-small cell cancer.
6. Can providers use lung cancer codes without biopsy confirmation?
Coding is based on a provider’s diagnosed condition and the care setting guidelines, respectively. Biopsy is not necessary for all coding, but outpatient coders cannot code an undetermined diagnosis.
7. Will the ICD-10 code for lung cancer impact reimbursement?
The diagnosis codes are required for necessity determination, coverage determination, and claims process. The actual reimbursement is related to the service, the care setting, and other payment policies.