ICD-10 Code for ER Positive HER2 Negative

Finding the right medical code can feel like navigating a maze. If you or someone you care about has been diagnosed with ER positive HER2 negative breast cancer, you might have come across the term “ICD-10 code” and wondered what it means.

You are not alone.

This guide walks you through everything you need to know about the ICD-10 code for ER positive HER2 negative breast cancer. We will keep things simple, clear, and useful — whether you are a patient trying to understand your medical records or a medical coder looking for accurate documentation.

Let us start with the basics.

What Does ER Positive HER2 Negative Mean?

Before we talk about codes, let us understand the condition itself.

ER Positive Explained

ER stands for estrogen receptor. When a breast cancer is ER positive, it means the cancer cells grow in response to the hormone estrogen. Think of estrogen as a key and the cancer cells as a lock. In ER positive cancer, the key fits the lock, and the cells multiply.

This is actually good news in many ways. ER positive cancers often respond well to hormone therapy, such as tamoxifen or aromatase inhibitors.

HER2 Negative Explained

HER2 stands for human epidermal growth factor receptor 2. It is a protein that controls cell growth. When cancer is HER2 negative, it means the cells do not have an excess of this protein.

HER2 negative cancers do not respond to targeted therapies like Herceptin (trastuzumab). But they also tend to be less aggressive than HER2 positive types in some cases.

Putting It Together

So ER positive HER2 negative means:

• The cancer uses estrogen to grow.

• The cancer does not overproduce the HER2 protein.

This is one of the most common subtypes of breast cancer. It is often treated with hormone therapy, surgery, radiation, and sometimes chemotherapy depending on the stage and grade.

Important note: The ICD-10 code alone does not usually specify both ER and HER2 status in one single code. Instead, coders use a combination of codes to paint the full picture.

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The Short Answer: Which ICD-10 Code for ER Positive HER2 Negative?

There is no single ICD-10 code that says “ER positive HER2 negative” all by itself. The ICD-10 system classifies cancer primarily by:

• Site (which breast, left or right)

• Laterality

• Encounter type (initial, subsequent, or sequela)

• Additional factors (like hormone receptor status)

However, for documentation and billing purposes, medical coders typically use:

• C50.911 – Malignant neoplasm of unspecified female breast (if side is unknown)

• C50.912 – Malignant neoplasm of unspecified male breast

• Then add an additional code for hormone receptor status: Z17.0 (estrogen receptor positive status)

For HER2 negative status, there is currently no standalone ICD-10 code for “HER2 negative.” Instead, the absence of HER2 positivity is implied in the medical record or documented with a Z17 code for HER2 negative when available (Z17.1 for HER2 positive, but HER2 negative is not directly coded in ICD-10 as of 2026).

Let me clarify that in the next section.

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Breaking Down the ICD-10 Codes Used

Below is a table to help you see how these codes work together in practice.

Current reality (2026): There is no official ICD-10-CM code for “HER2 negative.” Instead, if the cancer is not HER2 positive, the absence is usually noted in the pathology report but not given a separate diagnosis code. Some facilities use a Z code for “HER2 negative” under investigational or internal mappings, but this is not standard across all systems.

For accurate coding, always combine:

• Site and laterality code (C50 series)

• Estrogen receptor status (Z17.0)

• Clinical documentation that states HER2 negative in the chart

Why No Single Code for ER Positive HER2 Negative?

You might wonder: If this is such a common cancer type, why isn’t there one simple code?

Great question.

The ICD-10 system was designed before precision medicine became routine. It organizes diseases mainly by anatomy (where the cancer is) and behavior (malignant or benign). Hormone receptor and HER2 status are relatively recent discoveries in the grand history of medical coding.

As of 2026, the ICD-11 system (not yet widely adopted in the US) does a better job of including biomarker status. But in the United States and many other countries, ICD-10-CM is still the standard. So coders work with what exists.

Think of it like an address:

• C50.911 tells you the city and street (breast cancer)

• Z17.0 tells you the apartment number (ER positive)

• The medical notes tell you the color of the front door (HER2 negative)

You need all three to find the right house.

Step-by-Step Guide to Coding ER Positive HER2 Negative

Let us walk through a realistic scenario.

Case example:
A 58-year-old woman is diagnosed with invasive ductal carcinoma of the left breast. Pathology confirms:

• Estrogen receptor positive (ER+)

• Progesterone receptor positive (PR+)

• HER2 negative

Step 1 – Identify the primary site and laterality
Left breast, female → C50.012

Step 2 – Identify the hormone receptor status
ER positive → Z17.0

Step 3 – Document HER2 negative in the clinical record
No ICD-10 code for HER2 negative exists, but you should note in the chart: “HER2 negative by IHC/FISH.”

Final code set:
C50.012, Z17.0

That is it. Simple, clean, and billable.

Additional Codes You Might Need

Sometimes ER positive HER2 negative breast cancer requires other codes depending on the patient’s situation.

These are often used in addition to the breast cancer code and Z17.0.

Common Coding Mistakes to Avoid

Even experienced coders can make errors. Here are the most frequent pitfalls with ER positive HER2 negative coding.

Mistake #1: Looking for a single “perfect” code

There is none. Do not invent one. Use the combination method described above.

Mistake #2: Coding HER2 negative as Z17.1

Z17.1 means ER negative, not HER2 negative. This is a serious error that can affect treatment and research data.

Mistake #3: Forgetting laterality

If the pathology report says left breast, do not use C50.911 (unspecified). Always use the most specific code available.

Mistake #4: Using Z17.0 without pathology confirmation

Do not assume ER status. Only code Z17.0 when the pathology report explicitly states “estrogen receptor positive.”

Pro tip: Always keep the pathology report open when coding breast cancer. It is your roadmap.

How This Affects Billing and Reimbursement

You might be a patient looking at an insurance claim or a coder trying to get a claim paid. Either way, accurate coding matters.

Insurance companies use ICD-10 codes to decide:

• Whether a service is medically necessary

• How much they will reimburse

• Whether prior authorization is required

If you use the wrong code, the claim may be denied. For example:

• If you forget Z17.0, the payer might not understand why hormone therapy was prescribed.

• If you incorrectly use a metastasis code, the patient could be flagged as having stage IV cancer when they actually have early-stage disease.

Realistic advice: Double-check every code before submission. When in doubt, ask the oncologist or a certified medical coder.

A Note for Patients Reading This

If you are a patient, you do not need to memorize these codes. That is what medical billers and coders are for. But understanding them can help you:

• Read your own medical records with more confidence

• Catch potential errors in your insurance claims

• Have more informed conversations with your healthcare team

For example, if you see C50.012 and Z17.0 on your paperwork, you now know that means:

• Left breast cancer

• ER positive

If you do not see Z17.0, ask your doctor: “Was my estrogen receptor status documented in the coding?” Sometimes it is accidentally left out.

You are your own best advocate.

ER Positive HER2 Negative vs Other Subtypes

Let us compare this subtype to others. This table shows how coding differs.

Notice the gap? HER2 negative is not directly coded. That is why clear clinical documentation remains essential.

What About ICD-11? A Quick Look Ahead

The World Health Organization released ICD-11 in 2018, but adoption has been slow. In ICD-11, breast cancer coding is more granular.

For example, ICD-11 includes codes for:

• Luminal A-like (ER+, HER2-)

• Luminal B-like (ER+, HER2+)

• HER2+ (ER-)

• Triple negative

This will make life much easier for coders and researchers. However, as of 2026, the United States still uses ICD-10-CM. We are likely a few years away from a full transition.

Until then, the combination method (site code + Z17.0) is the correct approach.

Documentation Best Practices for Clinicians

Doctors and nurses, this section is for you. Your documentation directly affects coding accuracy.

What to always include in the medical record for ER positive HER2 negative cancer:

1. Exact location – Right breast, left breast, or both.

2. Laterality – Do not write “breast mass.” Write “right breast mass.”

3. Pathology results – ER positive, PR positive or negative, HER2 negative with method (IHC or FISH).

4. Stage and grade – If known.

5. Treatment plan – Hormone therapy, surgery, chemo, etc.

Example of good documentation:

“Patient is a 62-year-old female with newly diagnosed invasive ductal carcinoma of the left breast. Pathology from core needle biopsy on 4/10/2026 shows: ER positive (90%, strong), PR positive (80%, strong), HER2 negative (IHC 1+, FISH non-amplified). Clinical stage IIA (T2 N0 M0). Plan: Letrozole followed by breast-conserving surgery.”

That one paragraph gives a coder everything they need.

Frequently Asked Questions (FAQ)

1. Is there an ICD-10 code for ER positive HER2 negative breast cancer?

No, there is no single code. Use a site code (C50.xxx) plus Z17.0 for ER positive status. HER2 negative is documented in the clinical record but has no dedicated ICD-10 code.

2. What is the ICD-10 code for ER positive only?

Z17.0 – Estrogen receptor positive status.

3. What is the ICD-10 code for HER2 negative?

As of 2026, there is no official ICD-10-CM code for HER2 negative. This is a known limitation of the current coding system.

4. Can I use Z17.1 for HER2 negative?

No. Z17.1 means estrogen receptor negative. Using it for HER2 negative is incorrect and can cause billing or research errors.

5. Do I need to code HER2 status separately for insurance?

Usually no, because there is no code for HER2 negative. However, the pathology report should be attached to the claim if HER2 status affects treatment (e.g., deciding against Herceptin).

6. What is the difference between C50.911 and C50.012?

C50.911 is for unspecified female breast (side unknown). C50.012 is for left female breast. Always use the specific laterality code when known.

7. Will ICD-11 solve this problem?

Yes. ICD-11 includes specific codes for molecular subtypes, including ER+ HER2-. But the US has not yet adopted ICD-11 as of 2026.

Additional Resources

For further reading and official guidance, here are trusted sources:

• CMS ICD-10-CM Official Guidelines for Coding and Reporting
  Link: www.cms.gov/medicare/coding/icd10

• American College of Surgeons – Cancer Registry
  Link: www.facs.org/quality-programs/cancer/ncdb

• American Society of Clinical Oncology (ASCO) – Breast Cancer Coding Resources
  Link: www.asco.org/practice-policy/coding-reimbursement

These resources are free and updated annually. Bookmark them for reference.

Final Summary (Conclusion)

In three lines:

ER positive HER2 negative breast cancer is coded using a site-specific C50 code plus Z17.0 for ER positive status. There is no dedicated ICD-10 code for HER2 negative, so clear clinical documentation is essential. Accurate coding ensures proper billing, treatment tracking, and research data integrity.

Disclaimer:
This article is for informational and educational purposes only. It does not constitute medical advice, legal advice, or official coding guidance. Always consult a qualified medical coder, physician, or certified professional coder for specific coding decisions. Medical coding guidelines change over time. Verify all codes with the latest ICD-10-CM manual.

Author:
Professional Medical Coding Writer – Technical SEO Content Team

Date:
APRIL 13, 2026