Mastitis or breast cancer

1. Definition

• Mastitis → inflammation of the breast tissue, infective or non-infective; abscess → localised collection of pus
• Inflammatory breast cancer (IBC) → aggressive breast cancer with tumour cells blocking the dermal lymphatics; red, oedematous breast, often with no discrete mass
• The red breast → common presentation of both; cancer and inflammatory cancer can mimic infection

2. Why the difference matters

• Mastitis → treated in primary care or the emergency department with antibiotics
• IBC → rare, 1–5% of breast cancers, but the most aggressive subtype
• IBC treated as infection → weeks of antibiotics, delayed diagnosis, higher stage
• Neglected breast cancer → secondary inflammation and ulceration; looks infected, but is not classed as IBC
• Cancer can also sit under a true abscess → residual mass after drainage

3. Who gets it

Mastitis

• Lactational → breastfeeding women, mostly in the first 3 months; Staphylococcus aureus
• Periductal → younger women who smoke; mixed aerobic and anaerobic flora
• Duct ectasia → peri- and postmenopausal women
• Granulomatous → young parous women, oral contraceptive use

Breast cancer

• Lifetime risk → about 1 in 9 women in the UK; 1% of cases in men
• Risk rises with age; most over 50 years
• IBC → any age, including young women; any histology or receptor status
• Breast cancer in pregnancy and lactation → rare, presents late because changes are blamed on lactation

4. Clinical picture

Features that favour mastitis or abscess

• Lactating, cracked nipple, milk stasis
• Fever, rigors, malaise and raised white cell count
• Rapid onset over hours to days
• Wedge-shaped, tender, hot area
• Fluctuant tender mass → abscess
• Subareolar mass, seropurulent discharge, fistula at the areolar margin → periductal mastitis in a smoker
• Responds to antibiotics in 48–72 h

Features that favour inflammatory breast cancer

• Not lactating, no fever, white cell count normal
• Onset over weeks to 3 months
• Diffuse redness, warmth and swelling; erythema over a third of the breast or more
• Peau d'orange → skin oedema with dimpling at the hair follicles
• Breast feels heavy, firm, enlarged; pain may be mild
• Often no discrete lump
• Nipple flattening, inversion or crusting
• Hard, fixed axillary or supraclavicular nodes
• No response to antibiotics

Features of other breast cancer

• Painless, hard, irregular lump; tethered or fixed
• Skin dimpling, ulceration
• Nipple → Paget's disease (eczema-like change starting on the nipple), new inversion, bloody discharge
• Systemic → weight loss, bone pain, breathlessness

5. Signs that overlap

• Peau d'orange → seen in both IBC and acute mastitis
• Redness and warmth → both
• Tender axillary nodes → mastitis; hard, fixed nodes → cancer
• Nipple retraction → cancer, or slit-like retraction in periductal mastitis
• Lump → abscess (fluctuant, tender) or cancer (hard, irregular)

6. Investigations

Mastitis

• Full blood count, C-reactive protein
• Culture of milk or pus; MRSA (methicillin-resistant S. aureus) screen
• Ultrasound → abscess, size, loculation; guides aspiration
• Avoid mammography in the acute painful phase

Suspected cancer

• Triple assessment → clinical examination + imaging + core biopsy; accuracy about 99.6%
• Mammography and ultrasound → mass, calcifications, skin thickening; IBC may show only skin thickening
• Core biopsy → histology and oestrogen receptor, progesterone receptor and HER2 (human epidermal growth factor receptor 2) status
• Skin punch biopsy → tumour cells in the dermal lymphatics; a negative biopsy does not exclude IBC
• Ultrasound and biopsy of the axillary nodes
• IBC → staging with CT of chest, abdomen and pelvis and a bone scan, or PET-CT; IBC is stage III (T4d) at least
• MRI → breast extent when imaging is unclear

7. Management pathway

Mastitis

• Lactational → flucloxacillin, keep breastfeeding or expressing, analgesia
• Non-lactational → co-amoxiclav, or a macrolide plus metronidazole
• Abscess → ultrasound-guided aspiration, repeated until dry; incision and drainage if aspiration fails or the skin is thin
• No improvement in 48 h → ultrasound for abscess

When to suspect cancer

• No response to 1–2 courses of antibiotics
• Not lactating and no fever
• Residual mass after the infection settles
• Woman over 35–40 years with a first non-lactational "infection"
• Recurrent infection at the same site
• Hard, fixed axillary nodes

Cancer

• Urgent referral to a breast clinic for triple assessment
• IBC → trimodal treatment:
  1. Neoadjuvant chemotherapy (plus anti-HER2 therapy if HER2 positive)
  2. Modified radical mastectomy with axillary node clearance, no immediate reconstruction
  3. Post-mastectomy radiotherapy to the chest wall and nodes
• IBC → sentinel node biopsy not used (high false-negative rate); breast conservation not offered
• Endocrine therapy → oestrogen receptor positive tumours

Follow-up rule

• Re-examine every treated breast infection at 8–12 weeks
• Residual mass → triple assessment

8. Pitfalls

• Two courses of antibiotics in a non-lactating woman without a review → missed IBC
• Negative skin biopsy → IBC still possible; diagnosis is clinical
• Normal mammogram → does not exclude IBC
• Abscess in an older woman → biopsy the wall or the residual mass
• Lactating woman with a hard mass that does not settle → biopsy; pregnancy does not protect

Source

• Oxford Handbook of Clinical Surgery (McLatchie, Borley, Chikwe) → chapter 6, Breast and endocrine surgery
• Sheehan L, Skene A. Benign breast disorders → Surgery (Oxford) 2024; 42(12)
• Sabiston Textbook of Surgery, 22nd edition → chapter 68, Diseases of the Breast