What could be causing sharp pain under and around the left breast, which had previous breast cancer and radiation and chemotherapy, with pain worsening when sitting and alleviated by stretching?

Post-Radiation Musculoskeletal Pain Management in Breast Cancer Survivors

Most Likely Diagnosis

This patient's sharp, positional pain under the left breast that worsens with sitting and improves with stretching is most consistent with post-radiation musculoskeletal pain, specifically costochondritis or intercostal nerve injury, rather than cancer recurrence. 1

The key clinical features pointing away from malignancy include:

• Positional nature (worse sitting, better standing/stretching) indicates musculoskeletal origin 1
• Two-year stable duration without progression suggests benign etiology 1
• Relief with stretching is characteristic of chest wall pain, not malignancy 1

Critical First Step: Rule Out Recurrence

Despite the likely benign etiology, you must obtain diagnostic mammography with ultrasound immediately because this patient has focal, persistent pain in a previously treated breast. 1, 2

• Advanced cancers can present with pain as the only symptom, particularly invasive lobular carcinoma 1
• Focal noncyclical pain warrants imaging in women ≥30 years 2
• Pain related to prior surgery/radiation can mask recurrence 1

Treatment Algorithm After Imaging Excludes Malignancy

First-Line Management

Initiate scheduled multimodal non-opioid analgesia:

• Acetaminophen 650-1000mg every 6 hours PLUS ibuprofen 400-600mg every 8 hours (or naproxen 500mg twice daily) 1, 3
• This combination provides synergistic analgesia with opioid-sparing effects 3

Physical therapy with specific stretching exercises:

• Physical therapy has been demonstrated to be effective for post-surgical and post-radiation musculoskeletal symptoms 1
• An intensive exercise regimen resulted in 20% decrease in treatment-related pain 1
• Focus on pectoral stretches and intercostal muscle mobilization 1

Second-Line Options

Acupuncture for persistent symptoms:

• Multiple trials demonstrate efficacy in decreasing pain intensity in breast cancer survivors 1
• Meta-analyses show statistically significant improvement 1

Consider duloxetine 30-60mg daily if neuropathic component:

• Effective for neuropathic pain, numbness, and tingling in cancer survivors 1
• Particularly useful if radiation caused intercostal nerve injury 1

Specialist Referral Indications

Refer to physical medicine/occupational therapy if:

• Pain persists beyond 4-6 weeks despite NSAIDs and home exercises 1
• Functional limitations interfere with daily activities 1
• Chest wall tightness or restricted range of motion present 1

Common Etiologies in This Clinical Context

Post-radiation pain in breast cancer survivors stems from multiple mechanisms:

Musculoskeletal causes (most likely here):

• Costochondritis from radiation-induced inflammation 1
• Intercostal nerve injury from radiation, surgery, or ischemia 1
• Pectoral muscle spasm or strain 1
• Chest wall fibrosis from radiation 1

Nerve-related causes:

• Intercostal nerve entrapment (T3-T5 distribution supplies breast) 1
• Radiation-induced neuropathy 1
• Scar tissue nerve compression 1

Critical Pitfalls to Avoid

Do not dismiss pain without imaging in a cancer survivor:

• 25-60% of breast cancer survivors experience chronic treatment-related pain, but new or changing pain requires evaluation 1
• Invasive lobular and anaplastic carcinomas are disproportionately associated with pain 1

Do not assume all post-treatment pain is "normal":

• Focal, reproducible pain localized to one area warrants investigation 1
• Pain related to previous surgery is more common with postoperative complications or radiation 1

Do not start opioids as first-line therapy:

• Most pain in cancer survivors does not require strong opioids 4
• Multimodal non-opioid interventions should be the foundation 1, 3
• Reserve opioids strictly as rescue medication when non-opioid regimen fails 3

Do not overlook extramammary causes:

• 10-15% of "breast pain" originates from chest wall, spine, cardiac, pulmonary, or GI sources 1
• Intercostal nerve irritation anywhere along T3-T5 can refer pain to breast 1

Reassurance Component

After imaging excludes recurrence, provide explicit reassurance that pain alone rarely indicates cancer recurrence - this reassurance resolves symptoms in 86% of mild cases and 52% of severe cases. 5