What is the appropriate workup for a lump in the armpit?

Workup for an Axillary Lump

Begin with ultrasound of the axilla as the initial imaging modality, which can differentiate benign from malignant masses and determine if the lesion is solid or cystic. 1

Initial Clinical Assessment

Key historical features to elicit:

• Duration of the lump and whether it is increasing in size 1
• Associated symptoms: breast changes, nipple discharge, skin alterations, chest pain, arm swelling 1
• Constitutional symptoms: fever, weight loss, night sweats 2
• Personal history of breast cancer or other malignancies 1, 3
• Family history of breast, ovarian, or other cancers 1
• Recent infections, trauma, or breast procedures 4

Physical examination must include:

• Bilateral breast examination for masses, skin changes, nipple abnormalities 1, 5
• Assessment of both axillae for size, mobility, and characteristics of lymph nodes 1
• Examination of supraclavicular and cervical lymph nodes 1

Imaging Algorithm

First-Line Imaging: Axillary Ultrasound

Ultrasound of the axilla is the appropriate initial test because it can:

• Determine if the mass is solid, cystic, or a lipoma (which requires no further evaluation) 1
• Assess lymph node architecture and cortical thickness 1
• Guide subsequent biopsy if needed 1

Additional Imaging Based on Patient Age and Clinical Context

For women ≥40 years with an axillary lump:

• Perform diagnostic mammography to evaluate for an occult breast primary, as mammography can visualize portions of the axilla and detect underlying breast lesions 1, 5
• Mammography should be done even if ultrasound shows benign-appearing lymph nodes, as it provides global breast assessment 1, 5

For women <30 years:

• Proceed with targeted breast ultrasound without mammography to avoid unnecessary radiation 5
• Mammography has limited utility in this age group due to dense breast tissue 5

For men or patients with concerning features:

• Consider CT chest/abdomen/pelvis if there is suspicion for lymphoma, metastatic disease from non-breast primary, or systemic malignancy 1
• CT is not routinely indicated for isolated axillary masses without systemic symptoms 1

Tissue Diagnosis

When ultrasound findings are uncertain or suspicious, proceed to image-guided core needle biopsy (not fine-needle aspiration), as core biopsy provides superior sensitivity, specificity, and histological grading 2, 5

Indications for biopsy include:

• Enlarged lymph nodes with abnormal cortical thickening or loss of fatty hilum 1
• Solid masses that cannot be definitively characterized as benign 1
• Any mass in a patient with history of malignancy 6

Never perform biopsy before completing imaging, as biopsy-related changes will obscure subsequent image interpretation 5

Differential Diagnosis Considerations

The differential for an axillary lump is broad and includes:

Benign etiologies:

• Reactive lymphadenopathy from infection or inflammation 1
• Lipomas (require no further workup once identified on ultrasound) 1
• Accessory breast tissue or lactational changes 1
• Fat necrosis (can mimic malignancy) 7

Malignant etiologies:

• Metastatic breast cancer (most common malignant cause in women) 1
• Lymphoma or leukemia (especially with bilateral involvement) 1
• Metastases from other primaries (gastric cancer, melanoma, lung cancer) 6
• Occult breast cancer presenting as axillary adenopathy 1, 8

Critical Pitfalls to Avoid

• Do not assume an axillary lump is benign based on clinical examination alone—physical examination correctly identifies only about 85% of soft tissue masses 2
• Do not order MRI, PET, or advanced imaging as initial evaluation unless there is high suspicion for systemic malignancy or lymphoma 1, 5
• Do not delay imaging if the mass is increasing in size, as this is a red flag for malignancy 1
• Do not skip breast imaging in women presenting with isolated axillary adenopathy, as up to two-thirds of occult breast cancers can be detected with appropriate imaging 1

Management Based on Findings

If imaging shows clearly benign features (e.g., lipoma, normal lymph node architecture):

• Return to clinical follow-up only 2, 5
• No further imaging or biopsy needed 5

If imaging shows suspicious features:

• Proceed directly to image-guided core biopsy 1, 2, 5
• If malignancy is confirmed, assess hormone receptors and HER2 status 3

If breast cancer is suspected but no primary is identified:

• Consider breast MRI, which detects occult breast cancer in more than two-thirds of patients with axillary metastases 1