Primary lung cancer is coded in ICD-10-CM category C34, and the billable code depends on two facts in the record: which part of the lung is involved (main bronchus, upper, middle or lower lobe, overlapping sites or unspecified) and which side.
C34 itself, and its four-character subcategories C34.0, C34.1, C34.3, C34.8 and C34.9, are category headers that cannot go on a claim. You need the fifth character for laterality: 1 for right, 2 for left and 0 for unspecified side. The one exception is C34.2, middle lobe, which is billable as is, because only the right lung has a middle lobe.
Most lung cancer coding errors are not about the lobe, though. They come from mixing up primary and secondary (metastatic) disease, sequencing chemotherapy and immunotherapy encounters wrongly, moving to a history code too early, and billing low-dose CT screening without the tobacco-history codes Medicare expects.
This guide covers every C34 code in the FY2027 code set (in effect since October 1, 2026), the related codes that are often confused with them, the Official Guidelines that decide sequencing, and Medicare’s rules for lung cancer screening.
Key Takeaways
- Bill C34 codes at full specificity: lobe or bronchus plus side. C34.2 (middle lobe) has no laterality digit, and C34.21 does not exist.
- The lingula is part of the left upper lobe, so a lingular tumor is coded C34.12.
- Cancer that has spread to the lung from another organ is secondary: C78.01 (right), C78.02 (left) or C78.00 (unspecified), with the primary site coded too.
- Keep the active C34 code while treatment directed at the lung cancer continues. Use Z85.118 only after the cancer is excised or eradicated, treatment has ended and there is no evidence of disease.
- For an encounter chiefly for chemotherapy or immunotherapy, Z51.11 or Z51.12 goes first, followed by the C34 code.
- Medicare covers annual LDCT screening (CPT 71271) for eligible people aged 50 to 77 with at least 20 pack-years, after a G0296 counseling visit, and expects Z87.891 or an F17.21- code on the claim.
C34 Code Structure: Every Lung Cancer Code in FY2027
All titles below are the official ICD-10-CM long descriptions. Rows marked header are not valid for HIPAA claims.
| Code | Official title | Billable? |
|---|---|---|
| C34 | Malignant neoplasm of bronchus and lung | No, category header |
| C34.00 | Malignant neoplasm of unspecified main bronchus | Yes |
| C34.01 | Malignant neoplasm of right main bronchus | Yes |
| C34.02 | Malignant neoplasm of left main bronchus | Yes |
| C34.10 | Malignant neoplasm of upper lobe, unspecified bronchus or lung | Yes |
| C34.11 | Malignant neoplasm of upper lobe, right bronchus or lung | Yes |
| C34.12 | Malignant neoplasm of upper lobe, left bronchus or lung | Yes (includes lingula) |
| C34.2 | Malignant neoplasm of middle lobe, bronchus or lung | Yes (right side only by anatomy) |
| C34.30 | Malignant neoplasm of lower lobe, unspecified bronchus or lung | Yes |
| C34.31 | Malignant neoplasm of lower lobe, right bronchus or lung | Yes |
| C34.32 | Malignant neoplasm of lower lobe, left bronchus or lung | Yes |
| C34.80 | Malignant neoplasm of overlapping sites of unspecified bronchus and lung | Yes |
| C34.81 | Malignant neoplasm of overlapping sites of right bronchus and lung | Yes |
| C34.82 | Malignant neoplasm of overlapping sites of left bronchus and lung | Yes |
| C34.90 | Malignant neoplasm of unspecified part of unspecified bronchus or lung | Yes |
| C34.91 | Malignant neoplasm of unspecified part of right bronchus or lung | Yes |
| C34.92 | Malignant neoplasm of unspecified part of left bronchus or lung | Yes |
Right Lung Codes
The right lung has three lobes, so right-sided tumors can be coded to C34.11 (upper lobe), C34.2 (middle lobe) or C34.31 (lower lobe). A tumor of the right main bronchus is C34.01. If the record says only right lung, use C34.91, but go back to the CT, pathology or operative report first, because the lobe is almost always documented somewhere.
Left Lung Codes
The left lung has two lobes. A left upper lobe tumor, including one in the lingula, is C34.12. A left lower lobe tumor is C34.32, and the left main bronchus is C34.02.
Overlapping Sites and Bilateral Disease
Overlapping (.8). Use C34.81 or C34.82 when one contiguous tumor crosses lobe boundaries and the point of origin cannot be determined. Separate, non-contiguous tumors are not overlapping; code each site.
Both lungs. C34 has no bilateral code. The Official Guidelines say that when no bilateral code exists, you assign separate codes for the left and right side, for example C34.11 and C34.32. If it is unclear whether a second tumor is a separate primary or a metastasis, query the provider.
The guidelines also say codes for an unspecified side should rarely be used. Unspecified codes are not banned, but they invite CO-11 diagnosis-procedure mismatches when the procedure itself is side-specific, such as a right upper lobectomy.
Codes Commonly Confused With C34
| Code | Official title | Use it when |
|---|---|---|
| C78.00 to C78.02 | Secondary malignant neoplasm of unspecified, right or left lung | Cancer from another primary has spread to the lung |
| D02.20 to D02.22 | Carcinoma in situ of unspecified, right or left bronchus and lung | Pathology shows carcinoma in situ, not invasive cancer |
| C7A.090 | Malignant carcinoid tumor of the bronchus and lung | Pathology confirms a malignant carcinoid tumor |
| C45.0 | Mesothelioma of pleura | Pleural mesothelioma, which is not a lung primary |
| D38.1 | Neoplasm of uncertain behavior of trachea, bronchus and lung | Pathology states uncertain behavior |
| D49.1 | Neoplasm of unspecified behavior of respiratory system | A neoplasm is documented but its behavior is not specified |
| R91.1 | Solitary pulmonary nodule | Imaging shows a single nodule with no diagnosis yet |
| R91.8 | Other nonspecific abnormal finding of lung field | Lung mass or other nonspecific imaging finding |
| Z85.118 | Personal history of other malignant neoplasm of bronchus and lung | Prior lung cancer, treatment complete, no evidence of disease |
| Z85.110 | Personal history of malignant carcinoid tumor of bronchus and lung | Prior lung carcinoid, treatment complete |
Do not assign a C34 code for a suspicious nodule or mass on an outpatient claim before the provider documents a confirmed diagnosis. Section IV of the Official Guidelines prohibits coding probable, suspected or rule-out diagnoses in outpatient settings; code the finding (R91.1 or R91.8) or the symptoms instead, such as shortness of breath (R06.02) or a cough code from category R05. If the work-up documents low oxygen levels, our AHRF and hypoxemia ICD-10 guide explains when to use J96.01 versus R09.02.
Sequencing Rules for Lung Cancer Encounters
Chapter 2 of the FY2027 ICD-10-CM Official Guidelines (Section I.C.2) decides which code goes first. These are the rules that matter most for lung cancer claims.
Treatment directed at the primary. When the encounter is for treatment of the lung primary, such as surgery or a management visit, the C34 code is first-listed.
Treatment directed at a metastatic site only. When treatment targets the secondary site alone, for example radiation to brain metastases, the secondary code (C79.31) is first-listed and the primary C34 code follows.
Chemotherapy, immunotherapy or radiation. When the encounter is chiefly for one of these, Z51.11 (encounter for antineoplastic chemotherapy), Z51.12 (encounter for antineoplastic immunotherapy) or Z51.0 (encounter for antineoplastic radiation therapy) is listed first, followed by the cancer codes.
Anemia from the cancer. If the encounter treats only the anemia associated with the malignancy, sequence the malignancy first, followed by D63.0 (anemia in neoplastic disease).
Infusion encounters bring their own CPT and drug-unit rules on top of these diagnosis rules. Our infusion billing services page explains how we handle them.
Metastatic to Versus Metastatic From
Metastatic lung cancer is ambiguous wording. Cancer metastatic from the lung is a lung primary (C34.-) with secondary codes for the sites it has reached. Cancer metastatic to the lung is secondary (C78.0-), and the primary site is coded separately; if the primary is unknown, use C80.1, Malignant (primary) neoplasm, unspecified. When the note does not make the direction clear, query.
| Common spread site | Code | Official short title |
|---|---|---|
| Intrathoracic lymph nodes | C77.1 | Secondary and unspecified malignant neoplasm of intrathoracic lymph nodes |
| Brain | C79.31 | Secondary malignant neoplasm of brain |
| Bone | C79.51 | Secondary malignant neoplasm of bone |
| Liver | C78.7 | Secondary malignant neoplasm of liver and intrahepatic bile duct |
| Right adrenal | C79.71 | Secondary malignant neoplasm of right adrenal gland |
| Pleural effusion | J91.0 | Malignant pleural effusion (code the underlying neoplasm first) |
Current Cancer, History Code or Remission?
Under guideline I.C.2.m, the primary malignancy code is used until treatment is completed. That includes adjuvant chemotherapy or immunotherapy after a lobectomy, and the code stays active while treatment directed at the lung cancer is ongoing.
Z85.118 applies only when the primary has been excised or eradicated, no further treatment is directed to that site and there is no evidence of existing primary malignancy (guideline I.C.2.d). For a surveillance visit after completed treatment, report Z08 (encounter for follow-up examination after completed treatment for malignant neoplasm) with Z85.118, and add Z92.21 or Z92.3 if a history of chemotherapy or irradiation is relevant.
ICD-10-CM has remission codes only for certain blood cancers, such as leukemia and multiple myeloma. There is no in remission code for lung cancer, so if a note says lung cancer in remission, ask the provider whether the cancer is still current or is history.
Lung Cancer Screening: Medicare NCD 210.14
Medicare covers low-dose CT lung cancer screening under National Coverage Determination 210.14 (version 2, effective for dates of service on or after February 10, 2022). Coverage requires all of the following:
- Age 50 to 77.
- Asymptomatic, with no signs or symptoms of lung cancer.
- A tobacco smoking history of at least 20 pack-years.
- Currently smoking, or quit within the last 15 years.
- An order for lung cancer screening with LDCT.
Before the first screening, the beneficiary must have a counseling and shared decision-making visit, billed with HCPCS G0296. It must determine eligibility, use one or more decision aids, cover the need for annual screening, comorbidities and willingness to undergo diagnosis and treatment, and counsel the patient on quitting or staying off tobacco.
| Item | Medicare rule |
|---|---|
| G0296 | Counseling and shared decision-making visit; required before the first LDCT |
| CPT 71271 | Computed tomography, thorax, low dose for lung cancer screening, without contrast material(s); replaced G0297 on January 1, 2021 |
| Frequency | One 71271 per 12 months; at least 11 full months must pass after the last screening |
| Diagnosis codes | Z87.891 (personal history of nicotine dependence) for former smokers, or F17.210, F17.211, F17.213, F17.218 or F17.219 for current smokers |
| Patient cost | Part B deductible and coinsurance waived |
Many payers also expect Z12.2 (encounter for screening for malignant neoplasm of respiratory organs) as the reason for the screening; check each payer’s policy. If the screening finds a nodule, the guidelines allow the finding to be added as an additional diagnosis. A patient with symptoms such as hemoptysis is not a screening patient: the study is a diagnostic chest CT ordered for those symptoms, not 71271. Our radiology billing team checks these screening edits before claims go out, because a missing tobacco code or an age outside 50 to 77 tends to come back as a CO-50 medical necessity denial.
Worked Example: One Patient, Three Encounters
A 66-year-old former smoker has biopsy-proven adenocarcinoma of the right upper lobe with mediastinal node involvement and a single brain metastasis.
| Encounter | Codes in order | Why |
|---|---|---|
| Thoracic surgery consult | C34.11, C77.1, C79.31, Z87.891 | Care directed at the lung primary |
| Brain radiation (stereotactic) | C79.31, C34.11, C77.1 | Treatment directed at the metastatic site only |
| Immunotherapy infusion | Z51.12, C34.11, C77.1, C79.31 | Encounter chiefly for antineoplastic immunotherapy |
Two years later, after completed treatment, no evidence of disease and a surveillance CT, the visit would be Z08, Z85.118 and Z87.891. Surgical claims in this pathway, such as lobectomy and mediastinal staging, are covered on our cardiothoracic and thoracic surgery billing page.
How to Code a Lung Cancer Claim Step by Step
- Confirm the diagnosis. Look for pathology or a definitive provider statement. Without it, code the findings or symptoms.
- Decide primary or secondary. Read whether the cancer is metastatic from or to the lung, and query if it is not clear.
- Pick lobe and side. Use the imaging and operative reports to reach the fifth character; remember that C34.2 and the lingula are special cases.
- Add spread and complications. Code secondary sites, J91.0 for malignant effusion, and D63.0 when anemia in neoplastic disease is documented.
- Sequence by encounter purpose. Z51.11 or Z51.12 first for chemotherapy or immunotherapy, the secondary site first when only that site is treated, the C34 code first otherwise.
- Add tobacco status. Report Z87.891 or the F17.21- code that matches the documentation.
For a refresher on how diagnosis codes support CPT and HCPCS codes on the same claim, see understanding CPT, ICD-10 and HCPCS codes.
Oncology and pulmonology claims depend on sequencing that changes from visit to visit. Steady Medical Billing’s certified coders review every cancer encounter against the Official Guidelines before it reaches the payer.
Frequently Asked Questions
What is the ICD-10 code for lung cancer?
Primary lung cancer is coded in category C34. The billable code depends on the site and side, for example C34.11 for the right upper lobe, C34.32 for the left lower lobe and C34.2 for the middle lobe. C34.90 is used only when neither the site nor the side is documented.
What is the ICD-10 code for right lower lobe lung cancer?
C34.31, Malignant neoplasm of lower lobe, right bronchus or lung. The left lower lobe is C34.32.
Is there a code C34.21 for the right middle lobe?
No. The middle lobe code is C34.2, which is billable at four characters because only the right lung has a middle lobe. C34.21 does not exist and will be rejected.
When do I switch from C34 to Z85.118?
Use Z85.118 only after the lung cancer has been excised or eradicated, no further treatment is directed to that site and there is no evidence of disease. While treatment, including adjuvant chemotherapy or immunotherapy, continues, keep the active C34 code.
Which diagnosis codes go on a Medicare lung cancer screening claim?
Medicare expects Z87.891 for former smokers or F17.210, F17.211, F17.213, F17.218 or F17.219 for current smokers on G0296 and CPT 71271 claims. Many payers also expect Z12.2 as the screening reason.
