What is the most likely diagnosis and immediate management for a 56‑year‑old obese diabetic woman with hypertension and hyperlipidemia who presents with a 3 × 5 cm erythematous, warm, movable, blanching mass on the left lateral breast/axillary region that has been enlarging over 5 days, given her personal history of colon cancer and a sister with early‑onset breast cancer?

Differential Diagnosis and Immediate Management

This patient requires urgent diagnostic mammography with ultrasound and core needle biopsy within 48 hours to rule out inflammatory breast cancer (IBC), which must be excluded given the rapid onset (5 days), erythematous warm mass, and high-risk features including personal history of colon cancer and sister with early-onset breast cancer. 1

Most Likely Diagnoses (in order of priority)

1. Inflammatory Breast Cancer (IBC) - MUST BE EXCLUDED FIRST

This presentation meets several diagnostic criteria for IBC and requires immediate workup:

• Rapid onset: 5-day history meets the <6 month criterion 1
• Erythema with warmth: Classic IBC presentation 1
• Enlarging mass: Progressive growth over days is concerning 1
• High-risk patient: Personal history of colon cancer at age 48 and sister with breast cancer at age 30 significantly elevates risk 2
• Never had breast cancer screening: At age 56 with strong family history, this is a critical gap 1

Critical pitfall: IBC is commonly misdiagnosed as mastitis or abscess, leading to dangerous delays in treatment. The blanching borders and movability do NOT exclude IBC. 1

2. Breast Abscess/Infection

• Erythema, warmth, and pain are consistent with infection 1
• However, the 5-day rapid enlargement and lack of systemic symptoms (no fever mentioned) make simple infection less likely
• Diabetes increases infection risk but does not explain the specific presentation 3

3. Rapidly Growing Benign Lesion (Less Likely)

• Previous history of similar masses suggests possible recurrent lipomas or sebaceous cysts
• However, the erythema, warmth, and rapid growth in the breast/axillary region are atypical for benign lesions 4

Immediate Next Steps (Within 48-72 Hours)

1. Urgent Imaging Workup

Order immediately:

• Diagnostic bilateral mammography with accompanying ultrasound of both breasts and regional lymph nodes 1
• Focus on the left breast and left axillary region 1
• Document any skin thickening, architectural distortion, or suspicious masses 1

2. Tissue Diagnosis - MANDATORY

If imaging shows ANY suspicious features:

• Core needle biopsy of the mass (NOT fine needle aspiration) 1
• Skin punch biopsy (at least two specimens) from the erythematous area to evaluate for dermal lymphovascular invasion - pathognomonic for IBC when present 1
• Test all tissue for hormone receptors (ER/PR) and HER2 status 1

Critical point: Dermal lymphovascular emboli are pathognomonic for IBC but NOT required for diagnosis - clinical presentation with pathological confirmation of invasive carcinoma is sufficient. 1

3. If IBC is Confirmed - Immediate Staging

• CT chest/abdomen/pelvis and bone scan for systemic staging 1
• IBC is automatically staged as T4d, making it at least Stage IIIB disease 1
• PET/CT is not routinely recommended but may be considered 1

Management Algorithm

IF IBC is diagnosed:

1. Multidisciplinary tumor board referral immediately 1
2. Primary systemic chemotherapy with anthracycline + taxane regimen 1
3. Add trastuzumab if HER2-positive 1
4. Modified radical mastectomy after chemotherapy (breast conservation is contraindicated) 1
5. Postmastectomy radiation to 66 Gy given her age >45 years 1

IF infection/abscess:

• Ultrasound-guided aspiration or incision and drainage
• Broad-spectrum antibiotics covering skin flora
• Close follow-up in 48-72 hours to ensure resolution

IF benign lesion confirmed:

• Surgical excision given size >3 cm and patient anxiety 4
• Send for permanent pathology to confirm diagnosis 4

Critical Red Flags in This Case

1. No prior breast cancer screening at age 56 with first-degree relative diagnosed at age 30 - this patient should have been in high-risk screening 1, 4
2. Diabetes, hypertension, and obesity are associated with increased risk of advanced breast cancer including IBC 2
3. Personal history of colon cancer at age 48 raises concern for hereditary cancer syndrome 2
4. Rapid 5-day progression - benign lesions rarely grow this quickly 1
5. Location on lateral breast/mid-axillary line - this is a common site for breast cancer, not typical for simple sebaceous cysts 1

What NOT to Do

• Do NOT treat empirically with antibiotics without tissue diagnosis if IBC is suspected 1
• Do NOT delay imaging to "watch and wait" - every day counts with IBC 1
• Do NOT rely on the movability of the mass to exclude malignancy 1
• Do NOT assume this is a recurrent benign lesion based on remote history without tissue confirmation 1

Bottom line: This patient needs diagnostic mammography, ultrasound, and core needle biopsy with skin punch biopsy within 48 hours. IBC carries extremely poor prognosis if diagnosis is delayed, and this presentation cannot be dismissed as infection or benign disease without definitive tissue diagnosis. 1