• Schwartz's Principles of Surgery, 11th ed., describes MRM as preserving pectoralis major while removing level I, II, and sometimes level III axillary nodes.

Modified Radical Mastectomy (MRM)

1. The entire breast including most overlying breast skin, nipple, and areola
2. Pectoral fascia over the pectoralis major muscle
3. Axillary lymph nodes, usually level I and II, and occasionally level III when indicated
4. But preserves the pectoralis major muscle

What “modified” means

Axillary lymph-node levels

• Level I: nodes lateral to pectoralis minor
• Level II: nodes behind/between the borders of pectoralis minor
• Level III (apical): nodes medial to pectoralis minor, near the apex of the axilla

Indications

• Clinically palpable or biopsy-proven metastatic axillary lymph nodes
• Residual nodal disease after neoadjuvant systemic therapy in selected settings
• Locally advanced breast cancer
• Inflammatory breast cancer, typically after neoadjuvant chemotherapy, followed by post-mastectomy radiotherapy
• When breast-conserving surgery is unsuitable because of:
  • Large tumor relative to breast size
  • Multicentric disease
  • Persistently positive margins after attempted conservation
  • Contraindication to breast radiotherapy
  • Patient preference for mastectomy

Main operative steps

1. Anaesthesia and positioning
   The patient is placed supine, with the arm on the affected side positioned to expose the axilla.
2. Elliptical incision
   An elliptical incision is planned to remove the nipple-areola complex and any involved skin. It may extend toward the axilla to permit node dissection.
3. Raising skin flaps
   Skin flaps are elevated in the plane between subcutaneous fat and breast tissue. The usual limits are:
   • Superior: clavicle
   • Medial: lateral border of sternum
   • Inferior: inframammary fold/upper rectus sheath
   • Lateral: anterior border of latissimus dorsi
4. Removal of breast tissue
   The breast, including the axillary tail of Spence and pectoral fascia, is separated from the pectoralis major, which is retained.
5. Axillary lymph-node dissection
   The surgeon clears the axillary tissue while identifying and protecting key structures:
   • Axillary vein
   • Long thoracic nerve
   • Thoracodorsal nerve and vessels
   • Thoracodorsal pedicle
   • Where feasible, the intercostobrachial nerve
6. Drain insertion and closure
   One or more closed-suction drains are generally placed to decrease fluid collection, then flaps are closed.

Important structures and consequences of injury

Complications

Early complications

• Hemorrhage or hematoma
• Seroma, a collection of clear fluid beneath the flap
• Wound infection
• Skin-flap ischemia or necrosis
• Wound dehiscence
• Pain and restricted shoulder movement

Late complications

• Lymphedema of the ipsilateral arm
• Shoulder stiffness and reduced range of motion
• Chronic post-mastectomy pain syndrome
• Numbness of the upper inner arm
• Winged scapula if the long thoracic nerve is injured
• Cosmetic deformity and psychosocial effects
• Local recurrence or distant metastasis, depending on tumor biology and stage

Postoperative care

• Monitor the wound flaps, drain output, pain, and signs of infection or bleeding.
• Drains remain until output is low enough according to the surgical team’s protocol.
• Begin gentle arm and shoulder exercises early, as advised, to prevent stiffness.
• Pathology determines:
  • Tumor size and margin status
  • Number of lymph nodes removed and positive
  • ER, PR, and HER2 status
  • Need for adjuvant chemotherapy, endocrine therapy, HER2-targeted therapy, and/or radiotherapy.
• Reconstruction may be immediate or delayed, but immediate reconstruction is often avoided in inflammatory breast cancer because post-mastectomy radiotherapy is usually necessary.

One-line exam definition

Modified radical mastectomy is removal of the entire breast with pectoral fascia and axillary lymph-node dissection, while preserving the pectoralis major muscle.