What could be causing pain under the left breast radiating to the serratus anterior and into the axilla, accompanied by swollen lymph nodes in a patient?

Pain Under Left Breast Radiating to Serratus Anterior with Axillary Lymphadenopathy

This patient requires urgent age-appropriate diagnostic imaging (diagnostic mammogram with ultrasound if ≥30 years, ultrasound alone if <30 years) followed by core needle biopsy of the axillary lymph nodes to exclude malignancy, as focal unilateral breast pain with palpable axillary adenopathy has a significantly elevated cancer risk compared to isolated breast pain. 1

Immediate Diagnostic Approach

Clinical Triage

• This presentation is clinically significant and requires immediate workup because it combines focal (not diffuse) unilateral pain with swollen lymph nodes, which distinguishes it from benign cyclical mastalgia 1
• The cancer detection rate for focal breast pain alone is 2.3-4.6%, but the addition of axillary lymphadenopathy substantially increases malignancy risk 1
• Complete clinical evaluation must assess for other sites of adenopathy and potential non-breast etiologies before proceeding with breast-specific imaging 1

Imaging Protocol

• For patients ≥30 years: Perform diagnostic mammogram with targeted ultrasound of both the painful area and the axilla 1
• For patients <30 years: Ultrasound has 100% sensitivity and negative predictive value in this age group for focal breast symptoms, making it the preferred initial modality 1
• If imaging shows suspicious findings (BI-RADS 4 or 5), proceed immediately to core needle biopsy 1

Axillary Lymph Node Evaluation

• Core needle biopsy of abnormal axillary nodes is mandatory when imaging confirms suspicious characteristics (increased attenuation, high density, round/irregular shape, lack of hilar fat) 1, 2
• Among patients with palpable abnormal axillary nodes on mammography, 69% (9 of 13) had malignancies in one series, compared to only 1 malignancy among those with impalpable nodes 2
• If core biopsy reveals malignancy of breast origin but no breast mass is evident, proceed with breast MRI to identify occult primary tumor 1

Differential Diagnosis by Priority

Malignant Causes (Must Exclude First)

• Breast cancer with axillary metastases: Invasive lobular carcinoma and anaplastic carcinoma disproportionately present with pain as a primary symptom 1
• Occult breast cancer: In 31 patients with isolated axillary masses, 9 of 17 cancer cases had occult breast cancer, with 5 in the contralateral breast 1
• Lymphoma: Seven lymphomas were discovered among 22 patients with pathological axillary nodes on screening mammography, though only 13 of 60 newly diagnosed lymphomas in the region showed axillary involvement 2

Post-Surgical/Post-Radiation Complications (If Applicable)

• Persistent pain after breast cancer surgery (PPBCS): Chronic neuropathic pain affecting the serratus anterior region occurs in patients who had axillary node dissection, presenting as burning pain with numbness and hyperesthesia 3
• Cellulitis/lymphatic disruption: Occurs in approximately 1% of breast-conserving therapy patients, presenting with erythema, edema, tenderness, and warmth; can be relapsing and may occur before, during, or after radiation 4
• Post-surgical lymphatic interruption syndrome: Mimics infectious or neoplastic processes with erythema and edema, typically resolving over 2 months to 1 year without antibiotics 5

Benign Non-Malignant Causes

• Noncyclical mastalgia with reactive lymphadenopathy: Focal breast pain may be associated with benign findings (cysts, duct ectasia) that cause secondary lymph node enlargement 1
• Mondor disease: Thrombophlebitis of the thoracoepigastric vein can present as focal pain radiating along the chest wall 1
• Musculoskeletal causes: Serratus anterior muscle strain, intercostal nerve entrapment (T3-T5), or costochondritis can cause pain perceived as breast-related with reactive axillary nodes 1

Management Algorithm Based on Imaging Results

BI-RADS 1 (Negative) or 2 (Benign)

• If lymph nodes appear benign on imaging but remain palpable with high clinical suspicion, do not rely on negative imaging alone—proceed to biopsy 1
• Consider musculoskeletal evaluation and trial of NSAIDs for symptomatic relief 1, 6
• If simple cyst correlates geographically with pain, aspiration may provide symptom relief 1

BI-RADS 3 (Probably Benign)

• Perform imaging follow-up every 6 months for 1-2 years 1
• Provide symptomatic management with NSAIDs, supportive bra, ice/heat application 1, 6

BI-RADS 4 or 5 (Suspicious/Highly Suggestive)

• Immediate core needle biopsy is mandatory 1
• If malignancy confirmed, refer to NCCN Breast Cancer Guidelines for definitive management 1

Critical Pitfalls to Avoid

Do Not Dismiss as Benign Mastalgia

• Never provide reassurance alone without imaging when pain is focal and unilateral with lymphadenopathy 1, 6
• While breast pain alone has 0-3% cancer incidence, the addition of axillary adenopathy changes the clinical picture entirely 1

Do Not Delay Biopsy

• Palpable axillary mass with negative/benign imaging should still be managed based on clinical suspicion level 1
• Suspicion of lymphoma may require special pathologic evaluation or surgical excision rather than core biopsy 1

Do Not Overlook Post-Treatment Complications

• In patients with prior breast surgery, numbness occurs in 35%, pain in 30%, arm swelling in 15%, and infection/inflammation in 8% at 2-5 years post-operatively 7
• Radiation therapy significantly increases the frequency of arm/breast infection or inflammation (p=0.001) 7

Do Not Assume Infection Without Confirmation

• Cellulitis after breast-conserving therapy is relapsing in 80% of cases and may not respond to antibiotics if due to lymphatic disruption rather than infection 4, 5
• Axillary seromas requiring aspiration indicate a subset at higher risk for early cellulitis 4

Symptomatic Management (Only After Malignancy Excluded)

• Over-the-counter NSAIDs (ibuprofen) for pain control 1, 6
• Well-fitted supportive bra, especially during exercise 6, 8
• Ice packs or heating pads as needed 6, 8
• For persistent neuropathic pain after surgery, consider serratus plane block as an interventional option 3