Breast Imaging

ACR Workflow: How Should You Image the Axilla in Locally Recurrent Breast Cancer?

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ACR Workflow: How Should You Image the Axilla in Locally Recurrent Breast Cancer?

A 58-year-old female, ten years post-lumpectomy and radiation for early-stage breast cancer, presents for her annual mammogram. A new cluster of microcalcifications is identified near her surgical scar. Biopsy confirms an in-breast recurrence of her original cancer. As you plan her treatment, a critical question arises: has the cancer spread to her axillary lymph nodes? The next step is to choose the right initial imaging study to stage the axilla, a decision that will profoundly influence her surgical and systemic therapy. According to the American College of Radiology (ACR) Appropriateness Criteria, for this specific scenario, US axilla is rated ‘May be appropriate,’ representing the most effective initial step.

Who Fits This Clinical Scenario for Axillary Imaging?

This guidance is specifically for a female patient with a new, pathologically-confirmed local recurrence of breast cancer. This includes recurrence within the breast tissue (in-breast) or on the chest wall following a mastectomy. The key element is that this is the initial imaging of the axilla for this new recurrent event, performed after the recurrence has been diagnosed by mammography, digital breast tomosynthesis (DBT), or other imaging, and confirmed by biopsy.

This workflow is distinct from several related but different clinical situations. This article does not apply to:

  • Patients with a new, primary (first-time) diagnosis of breast cancer. The imaging workup for the axilla in these cases is stratified by tumor size and clinical node status, following different ACR guidelines.
  • Patients presenting with a new palpable axillary lump without a known breast cancer diagnosis. This presentation requires a different diagnostic algorithm to determine the cause of the axillary mass itself.
  • Patients being evaluated for suspected distant metastatic disease. While axillary status is part of the overall picture, the primary imaging question in that scenario is systemic staging, which may involve different modalities.

Applying this guidance is contingent on having a confirmed local recurrence as the starting point for the axillary evaluation.

What Diagnoses Are You Working Up in This Scenario?

When evaluating the axilla in a patient with locally recurrent breast cancer, the primary goal is to determine the presence and extent of regional nodal disease. This assessment is crucial for staging and directly impacts treatment planning, including the scope of surgery, the design of radiation fields, and the choice of systemic therapies.

The most critical diagnosis to confirm or exclude is axillary nodal metastasis. This signifies that cancer cells from the local recurrence have traveled through lymphatic channels and established a secondary tumor within one or more axillary lymph nodes. The presence of nodal metastases upstages the disease and generally indicates a more aggressive biology, often necessitating more intensive treatment, such as an axillary lymph node dissection and adjuvant systemic therapy.

A key alternative consideration is benign reactive lymphadenopathy. Lymph nodes can become enlarged and prominent due to non-malignant causes, including inflammation from the biopsy procedure itself, post-surgical changes from the original cancer treatment, or effects of prior radiation therapy. Differentiating these benign changes from true metastases is a primary function of the imaging study and any subsequent biopsy.

Less commonly, you may be evaluating for recurrence in an intramammary lymph node, which is a node located within the breast parenchyma itself. While technically not an axillary node, its involvement carries prognostic significance and can be detected during a comprehensive evaluation. Finally, extensive post-treatment scar tissue or fat necrosis can sometimes mimic nodal masses, and imaging helps distinguish these benign entities from true recurrence.

Why Is Axillary Ultrasound the Recommended Initial Study?

For the initial evaluation of the axilla in a patient with locally recurrent breast cancer, the ACR designates axillary ultrasound (US) as ‘May be appropriate.’ This is the highest rating assigned to any initial imaging modality in this specific context, making it the preferred first step. The rationale is based on its diagnostic capability, safety profile, and ability to guide immediate intervention.

Axillary US offers excellent spatial resolution, allowing for detailed morphologic assessment of lymph nodes. Radiologists look for specific features suggestive of malignancy, such as cortical thickening, a rounded (rather than oval) shape, and the loss or effacement of the central fatty hilum. This high-resolution view is highly sensitive for detecting suspicious nodes.

Crucially, ultrasound’s greatest advantage is its ability to facilitate real-time, image-guided biopsy. If a suspicious node is identified, a fine-needle aspiration (FNA) or core needle biopsy can be performed during the same appointment. This provides a rapid, minimally invasive method to obtain a definitive pathologic diagnosis, which is essential for accurate staging and treatment planning. Furthermore, US involves no ionizing radiation (adult radiation relative level: O 0 mSv) and does not require intravenous contrast agents.

Other advanced imaging modalities are also rated for this scenario but are not the typical first choice for focused axillary evaluation:

  • MRI breast without and with IV contrast is also rated ‘May be appropriate.’ It provides a comprehensive view of the recurrent tumor, the entire breast, chest wall, and axilla. However, it is more costly, takes longer to perform, and cannot be used to guide a biopsy in the same session. It is often used to assess the extent of the parenchymal recurrence, with the axillary evaluation being a secondary benefit.
  • FDG-PET/CT skull base to mid-thigh is also ‘May be appropriate’ but serves a different purpose. It is a whole-body systemic staging tool used to detect distant metastases. While it can identify avid axillary nodes, its spatial resolution is lower than ultrasound for detailed nodal morphology, and it involves a significant radiation dose (adult RRL: ☢☢☢☢ 10-30 mSv). It is typically reserved for patients with biopsy-proven nodal disease or other high-risk features.
  • CT of the chest, abdomen, and pelvis is rated ‘Usually not appropriate’ for the initial axillary assessment due to lower sensitivity for subtle nodal disease compared to US and its associated radiation exposure.

What’s Next After Axillary Ultrasound? Downstream Workflow

The results of the axillary ultrasound and any subsequent biopsy create a clear branching point in the patient’s management plan. The downstream workflow is logical and directed by the pathologic findings.

If the ultrasound is positive (suspicious nodes identified):
The immediate next step is an ultrasound-guided biopsy (FNA or core needle).

  • If the biopsy confirms malignancy, the patient is now pathologically node-positive. This finding is a major determinant of subsequent therapy. It typically necessitates a more extensive axillary surgery, such as an axillary lymph node dissection (ALND), rather than a less invasive sentinel lymph node biopsy (SLNB). It also strongly influences decisions regarding adjuvant chemotherapy, targeted therapy, and the scope of radiation treatment. Systemic staging with FDG-PET/CT is often considered at this point to rule out distant disease.
  • If the biopsy is benign, but the node remains highly suspicious on imaging, a discussion between the radiologist, surgeon, and oncologist is warranted to decide between short-term imaging follow-up or surgical excisional biopsy.

If the ultrasound is negative (no suspicious nodes found):
A negative ultrasound does not definitively rule out microscopic nodal disease. The patient is considered clinically node-negative, but pathologic confirmation is still required. The standard next step is to proceed with a sentinel lymph node biopsy (SLNB) at the time of the surgical resection of the local recurrence. The results of the SLNB will provide the definitive pathologic nodal stage and guide further adjuvant therapy decisions.

Common Pitfalls to Avoid in Axillary Staging for Recurrence

Navigating the workup for recurrent breast cancer requires careful attention to detail to avoid common errors that can impact staging and treatment.

First, do not assume a negative ultrasound is definitive. A normal-appearing axillary ultrasound can harbor microscopic metastases. Failing to proceed with a sentinel lymph node biopsy (SLNB) in a patient with a negative US can lead to significant under-staging and, consequently, under-treatment.

Second, be aware of the challenge of interpreting post-treatment changes. The anatomy of the axilla is often altered by prior surgery and radiation. Scar tissue, seromas, and radiation-induced fibrosis can mimic or obscure suspicious lymph nodes. This makes interpretation highly dependent on the experience of the radiologist, who must be provided with a detailed clinical history.

Third, consider the adequacy of the biopsy sample. While FNA is often sufficient for a diagnosis, a core needle biopsy may be preferred if more tissue is needed for ancillary testing, such as confirming the hormone receptor (ER/PR) and HER2 status of the metastatic deposit, which can sometimes differ from the primary tumor.

Finally, avoid premature systemic staging. Ordering a PET/CT before confirming nodal pathology can lead to ambiguity. The focused, high-resolution assessment with ultrasound and guided biopsy should precede whole-body imaging unless there are other strong indications of distant disease.

Related ACR Topics and Tools

This article covers one specific variant within the broader topic of axillary imaging. For a comprehensive overview of all clinical scenarios, from palpable lumps to staging for primary breast cancer, please consult our parent guide. Additionally, several tools can assist in applying these criteria and understanding the recommended studies.

Frequently Asked Questions

Why not order a PET/CT for every patient with recurrent breast cancer?

FDG-PET/CT is a tool for systemic staging to find distant disease, not for high-resolution initial evaluation of the axillary lymph nodes. Axillary ultrasound provides superior detail of nodal morphology and, critically, allows for immediate image-guided biopsy. PET/CT is often used after nodal status is confirmed by biopsy or if there is a high clinical suspicion of widespread disease. It also involves a significant radiation dose that is unnecessary if the goal is only to evaluate the axilla.

If the patient already had a full axillary dissection, is ultrasound still useful?

Yes, it is still the recommended initial study. Recurrence can occur in any remaining soft tissue within the dissected axillary bed, in the scar tissue, or in adjacent, non-traditional nodal basins like the supraclavicular or internal mammary regions. Ultrasound is excellent for evaluating these areas for new, suspicious nodules.

What specific features make a lymph node ‘suspicious’ on ultrasound?

Key morphologic features that raise suspicion for malignancy include a loss of the normal oval or kidney-bean shape (becoming rounded), asymmetric or diffuse thickening of the outer cortex, and the compression or complete loss of the central bright fatty hilum. Increased blood flow on color Doppler imaging can also be a suspicious sign.

Is breast MRI a reasonable first choice instead of ultrasound for the axilla?

Breast MRI is also rated ‘May be appropriate’ by the ACR and is a valid choice. It provides an excellent overview of the extent of the recurrence within the breast or chest wall and visualizes the axilla well. However, for the specific task of evaluating and biopsying the axillary nodes, ultrasound is often faster, more accessible, and enables a same-day procedure. The choice may depend on whether the primary clinical question is about the extent of the breast recurrence (favoring MRI) or specifically staging the axilla (favoring US).

How does prior radiation to the axilla affect the ultrasound evaluation?

Prior radiation makes the ultrasound interpretation more challenging. It can cause fibrosis, scarring, and architectural distortion, which can obscure nodes or mimic malignancy. It can also alter lymphatic drainage patterns. The fundamental imaging approach (ultrasound first) does not change, but it is critical that the radiologist is fully aware of the patient’s treatment history to interpret the findings in the correct clinical context.

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 29, 2026