What are the possible causes and treatments for a persistent and occasionally tender lump under the armpit (axilla)?

Axillary Lump Present for Years with Intermittent Tenderness

For a long-standing axillary lump with intermittent tenderness, you should obtain axillary ultrasound as the initial imaging study, followed by diagnostic mammography if you are ≥30 years old, to differentiate between benign causes (most likely reactive lymphadenopathy, lipoma, or sebaceous cyst) and the less common possibility of malignancy. 1, 2

Initial Imaging Strategy

The chronicity of your lump (present for years) significantly lowers the probability of aggressive malignancy, but does not exclude it entirely. 1

For patients ≥30 years:

• Obtain axillary ultrasound as the primary imaging modality to characterize the mass (solid versus cystic, lymph node morphology, presence of fatty hilum) 3, 1
• Obtain diagnostic mammography and/or digital breast tomosynthesis at the same visit to evaluate for an occult breast primary lesion that could have metastasized to the axilla 1, 2
• The mammogram must include standard views plus magnification views to identify any microcalcifications 2

For patients <30 years:

• Start with targeted ultrasound only to avoid unnecessary radiation exposure in this lower-risk age group 2

Most Likely Diagnoses Based on Your Presentation

The intermittent tenderness and years-long duration suggest several benign possibilities:

Benign reactive lymphadenopathy:

• Most common benign cause of axillary masses 4
• Can wax and wane with infections, causing intermittent tenderness 1
• Ultrasound will show preserved fatty hilum in benign nodes 1

Lipoma:

• Common benign soft tissue tumor that can occur in the axilla 5, 6
• Can become tender with size or compression of adjacent structures 5
• Ultrasound shows homogeneous fatty mass 5

Epidermal inclusion cyst:

• Frequently encountered in the axilla 6
• Can become intermittently inflamed and tender 6

When to Proceed with Biopsy

You need ultrasound-guided core needle biopsy (not fine needle aspiration) if: 1

• The lymph node lacks a fatty hilum (90-93% positive predictive value for malignancy) 1
• The mass shows suspicious features on ultrasound despite the chronic presentation 1
• Clinical concern persists even if imaging appears benign 1

Core biopsy is superior to FNA because it provides architectural information crucial for distinguishing reactive lymphadenopathy from lymphoma and allows immunohistochemical studies (sensitivity 88%, specificity 98-100% versus FNA sensitivity 74%) 1

Critical Pitfalls to Avoid

Do not assume chronicity automatically means benign disease:

• Some malignancies, including lymphoma and indolent breast cancers, can present as slowly growing masses 1, 4
• Phyllodes tumors can enlarge rapidly after years of stability 3

Do not rely on negative ultrasound alone:

• Axillary ultrasound has relatively low negative predictive value when used in isolation 1
• The combined negative predictive value of mammography plus ultrasound exceeds 97% 2

Do not perform mammography alone without ultrasound:

• Mammography has a high false-negative rate for detecting axillary lymphadenopathy 1

Do not delay biopsy if imaging shows absence of fatty hilum:

• This finding has 90-93% positive predictive value for malignancy regardless of symptom duration 1

Follow-Up Strategy if Initial Workup is Benign

If imaging and/or biopsy confirm benign disease:

• Treat any underlying infection or inflammatory condition appropriately 1
• Consider short-interval follow-up ultrasound (typically 6 months) to document stability or resolution 1
• Any growth or change in character warrants repeat biopsy 1