What is the management for a patient with a history of mastectomy on one side due to breast cancer and now diagnosed with breast cancer on the other side?

Management of Contralateral Breast Cancer After Prior Mastectomy

For a patient with a history of mastectomy on one side who now develops breast cancer on the contralateral side, the standard surgical approach is total mastectomy of the affected breast with sentinel lymph node biopsy for axillary staging, followed by systemic therapy based on tumor biology. 1, 2

Initial Diagnostic Workup

Each breast lesion requires independent pathologic confirmation via core needle biopsy before any surgical intervention. 2 The pathologic assessment must include:

• Histological type and grade 3
• Estrogen receptor (ER) and progesterone receptor (PR) status by immunohistochemistry 3, 2
• HER2 status using FDA-approved companion diagnostic tests 3, 4
• Ki67 proliferation markers 2

Perform diagnostic mammography of the remaining breast to identify extent of disease and rule out additional lesions. 2 Breast MRI may be appropriate as a screening tool for the contralateral breast in patients with prior mastectomy history. 3

Complete staging workup includes:

• Physical examination focusing on family history and genetic risk factors 1, 2
• Complete blood count and routine chemistry 3
• Chest imaging (X-ray or CT) 2
• Abdominal ultrasound or CT for higher-risk disease 2
• Bone scan for stage IIB-III disease 2

Genetic counseling is mandatory given the bilateral presentation, particularly to assess for BRCA1/2 mutations. 3, 1, 2 The lifetime risk of contralateral breast cancer in BRCA1 mutation carriers ranges from 25% to 31% over 10 years. 3

Surgical Management

Standard Approach: Total Mastectomy

Bilateral total mastectomy with removal of all breast tissue is the recommended surgical approach for patients with bilateral malignant breast masses. 1, 2 Since the patient already had mastectomy on one side, this translates to total mastectomy of the remaining breast with cancer. 1

Sentinel lymph node biopsy (SLNB) is the standard of care for axillary staging when invasive cancer is present. 3, 1, 2 SLNB should be performed rather than complete axillary lymph node dissection unless there is proven metastatic disease. 3, 1, 2

Immediate breast reconstruction is appropriate and should be discussed with all patients. 3, 1, 2

Alternative Consideration: Breast Conservation

Breast conservation therapy is feasible only when ALL of the following criteria are met:

• Clear surgical margins achievable (at least 2 mm for DCIS) 3
• Tumor size relative to breast volume allows adequate resection 3
• Absence of multicentric disease 3
• No prior chest wall irradiation 3
• Patient can tolerate mandatory whole breast radiation therapy 2

However, breast conservation is generally discouraged in this clinical scenario because the patient has already demonstrated bilateral breast cancer susceptibility, suggesting higher genetic or familial risk. 3 Mastectomy provides definitive local control without the need for radiation therapy, which may be particularly important given the patient's history. 3

Systemic Therapy Decisions

Treatment decisions must be based on the biological characteristics of the new cancer, considering tumor stage, hormone receptor status, HER2 status, and axillary lymph node involvement. 1, 2

For hormone receptor-positive tumors (ER+ or PR+):

• Endocrine therapy is mandatory 2, 5
• Tamoxifen is effective in premenopausal and postmenopausal women with metastatic breast cancer 5
• Aromatase inhibitors are alternatives for postmenopausal women 2

For HER2-positive tumors:

• Anti-HER2 therapy (trastuzumab) plus chemotherapy 2, 4
• Trastuzumab is indicated for adjuvant treatment of HER2-overexpressing node-positive or high-risk node-negative breast cancer 4

For triple-negative tumors:

• Chemotherapy is the mainstay 2
• Consider immunotherapy if PD-L1 positive 2

Radiation Therapy

For mastectomy patients, post-mastectomy radiation therapy is recommended for:

• Four or more positive axillary nodes 3
• T3-T4 tumors 3
• One to three positive axillary lymph nodes, especially with additional risk factors 3

Post-mastectomy radiation therapy should be considered for patients with one to three positive axillary lymph nodes. 3, 2

Special Considerations for BRCA Mutation Carriers

BRCA1/2 carriers face a 25-31% 10-year risk of developing new breast cancer. 3 With bilateral mastectomy (completing the second side), the risk for subsequent breast cancer incidence is reduced by 90-95%. 3, 2

Risk-reducing salpingo-oophorectomy should be considered per genetic/familial high-risk assessment guidelines. 3, 1, 2 This is particularly important as BRCA mutation carriers have elevated ovarian cancer risk. 3

Post-Treatment Surveillance

Annual clinical examinations of the chest/reconstructed breast are recommended after bilateral mastectomy. 1, 2 There remains a small risk of developing breast cancer even after bilateral mastectomy. 1

Mammograms are NOT recommended after bilateral mastectomy. 1, 2 This is because there is no remaining breast tissue to image. 1

Focus surveillance on:

• Detection of locoregional recurrence 3
• Systemic metastases (particularly in first 2 years after surgery when risk is highest) 6
• Routine health maintenance 1

Critical Pitfalls to Avoid

Never perform unilateral mastectomy when bilateral malignancy is confirmed—the risk is equal in both breasts. 1, 2 In this case, since one mastectomy was already performed, complete the bilateral mastectomy by removing the remaining breast with cancer.

Do not delay tissue biopsy, as this delays treatment of malignancy. 1, 2

Do not omit genetic counseling in bilateral breast cancer, as this presentation strongly suggests possible hereditary cancer syndrome. 3, 1, 2 The bilateral presentation warrants mandatory genetic assessment. 3

Do not routinely perform imaging to evaluate for distant disease in asymptomatic patients with a history of breast cancer. 3 However, for newly diagnosed stage IIB-III disease, staging imaging is appropriate. 3

Avoid complete axillary lymph node dissection in the absence of proven metastatic disease. 1, 2 Sentinel lymph node biopsy provides adequate staging with significantly less morbidity (pain, lymphedema, sensory loss). 3