What is the recommended workup for an axillary (armpit) lump?

Workup for Axillary Lump

Axillary ultrasound is the initial imaging modality of choice for evaluating any axillary lump, whether unilateral or bilateral, and should be complemented by diagnostic mammography in women ≥30-40 years to exclude an occult breast primary. 1, 2, 3

Initial Clinical Evaluation

The clinical assessment must determine:

• Duration and growth pattern – Progressive enlargement over weeks to months raises concern for malignancy 3
• Associated symptoms – Presence of hyperemia suggests infection/inflammation but does not exclude inflammatory breast cancer; assess for breast masses, nipple discharge, skin changes, arm swelling, or systemic symptoms 2, 3
• Personal cancer history – Prior breast cancer significantly increases risk of metastatic disease 3
• Family history – Breast, ovarian, or other hereditary cancers elevate suspicion 3
• Bilateral breast and axillary examination – Assess for masses, skin changes, nipple abnormalities, and lymph node characteristics (size, mobility, texture) 3

Imaging Algorithm

Step 1: Axillary Ultrasound (Always First)

Ultrasound is "usually appropriate" (ACR rating 8-9) for initial imaging of any palpable axillary lump. 1, 2, 3

Ultrasound evaluates:

• Whether the mass is solid, cystic, or lipomatous 3
• Lymph node architecture: cortical thickness, presence/absence of fatty hilum 1
• Surrounding soft tissue inflammation and vascular flow patterns 2

Key ultrasound features suggesting malignancy:

• Short-axis diameter >1 cm 1
• Cortical thickness >0.3 cm 1
• Absence of fatty hilum (highest predictive value: 90-93% PPV for malignancy) 1, 2

Step 2: Diagnostic Mammography ± Digital Breast Tomosynthesis

For women ≥30-40 years, diagnostic mammography and/or DBT should complement axillary ultrasound to evaluate for an occult breast primary. 1, 2, 3

• Mammography provides global breast assessment but has high false-negative rate for axillary lymphadenopathy itself 1, 2
• DBT is superior to standard mammography for detecting subtle architectural distortion 1
• DBT increases breast cancer detection rates, particularly in women 40-49 years 1

Critical caveat: Mammography is not optimal for evaluating the axilla itself and should never be used alone without ultrasound 1, 2

Tissue Diagnosis Strategy

When to Biopsy

Proceed directly to image-guided core needle biopsy if:

• Ultrasound shows suspicious features (absent fatty hilum, cortical thickening >0.3 cm, size >1 cm) 1, 2
• Clinical concern persists despite benign-appearing imaging 2
• Solid mass cannot be definitively characterized as benign 3

Biopsy Technique

Ultrasound-guided core needle biopsy is superior to fine needle aspiration. 1, 2, 3

• Core biopsy: 88% sensitivity, 98-100% specificity 1, 2
• FNA: 74% sensitivity, 98-100% specificity 1, 2
• Core biopsy provides architectural information crucial for distinguishing reactive lymphadenopathy from lymphoma and allows immunohistochemical studies 2
• FNA may be appropriate if patient cannot discontinue anticoagulation 1

Important limitation: When combined with ultrasound, biopsy sensitivity improves from 61% to 79%, but negative ultrasound with or without biopsy does not rule out nodal disease 1, 2

Management Based on Results

If Imaging Shows Clearly Benign Features

• Return to clinical follow-up only, no further imaging or biopsy needed 3

If Benign/Reactive Lymphadenopathy Confirmed

• Treat underlying infection or inflammatory condition 2
• Consider short-interval follow-up ultrasound to document resolution 2

If Malignancy of Breast Origin Diagnosed

• Assess hormone receptors and HER2 status 2, 3
• If no breast primary identified on mammography/ultrasound, proceed with breast MRI (detects occult breast cancer in >66% of patients with axillary metastases) 2, 3
• Follow NCCN Guidelines for Breast Cancer management 2

If Lymphoma Suspected

• Special pathologic evaluation and/or surgical excision may be required rather than core biopsy alone 2

Critical Pitfalls to Avoid

• Never assume hyperemia indicates benign disease – malignancy can present with overlying skin changes 2
• Never rely on negative ultrasound alone – axillary ultrasound has relatively low negative predictive value and sensitivity 1, 2
• Never perform mammography alone without ultrasound – mammography has high false-negative rate for axillary lymphadenopathy 1, 2
• Never delay biopsy if suspicious features present – absence of fatty hilum has 90-93% PPV for malignancy 1, 2

Differential Diagnosis Considerations

The axilla contains lymph nodes plus non-lymphatic tissue (accessory breast tissue, skin, fat, muscles, nerves, vessels), creating a wide differential 4:

Benign etiologies: Reactive lymphadenopathy, lipomas, accessory breast tissue, hamartoma, pseudoangiomatous stromal hyperplasia (PASH) 3, 4, 5, 6

Malignant etiologies: Metastatic breast cancer (including from accessory breast tissue), lymphoma, leukemia 3, 7, 8