From the Guidelines
The probability of contralateral breast cancer (CBC) in this 64-year-old woman with asymmetry on mammogram of the right breast 7 years after left mastectomy is approximately 0.5-1% per year, or about 3.5-7% cumulative risk at this point. This risk is higher than the general population but varies based on several factors including her original cancer's characteristics, genetic predisposition, and treatment history 1. The asymmetry on mammogram warrants prompt diagnostic evaluation with additional imaging (diagnostic mammogram, ultrasound) and possibly biopsy, as it represents a concerning finding. Risk factors that may increase her CBC probability include BRCA1/2 mutations (which increase lifetime risk to 30-40%), young age at first diagnosis, lobular histology in the original cancer, and family history of breast cancer. Prior treatments such as tamoxifen or aromatase inhibitors may have reduced her risk somewhat 1. The 7-year timeframe is significant as most recurrences and contralateral cancers occur within the first 5-10 years after initial diagnosis, placing her in a higher-risk window 1. Diagnostic evaluation should not be delayed as early detection significantly improves outcomes for second primary breast cancers. Some key points to consider in her management include:
- The role of breast MRI in screening women with a history of breast cancer is still being investigated, but may be considered in high-risk cases 1.
- The use of hormone replacement therapy (HRT) increases the risk of recurrence and should be discouraged 1.
- Regular exercise and maintenance of a healthy weight are recommended to reduce the risk of recurrence and improve overall prognosis 1. Given the most recent evidence from 2021, prompt diagnostic evaluation and consideration of risk-reducing strategies are essential in managing this patient's care 1.
From the FDA Drug Label
The incidence of contralateral breast cancer is reduced in breast cancer patients (premenopausal and postmenopausal) receiving tamoxifen compared to placebo. In clinical trials with tamoxifen of 1 year or less, 2 years, and about 5 years duration, the proportional reductions in the incidence rate of contralateral breast cancer among women receiving tamoxifen were 13% (NS), 26% (2p = 0.004) and 47% (2p < 0.00001), with a significant trend favoring longer tamoxifen duration (2p = 0. 008). Treatment with about 5 years of tamoxifen reduced the annual incidence rate of contralateral breast cancer from 7.6 per 1,000 patients in the control group compared with 3. 9 per 1,000 patients in the tamoxifen group. In the NSABP B-14 trial in which patients were randomized to tamoxifen 20 mg/day for 5 years vs. placebo, the incidence of second primary breast cancers was also significantly reduced (p < 0.01). In NSABP B-14, the annual rate of contralateral breast cancer was 8.0 per 1,000 patients in the placebo group compared with 5. 0 per 1,000 patients in the tamoxifen group, at 10 years after first randomization.
The probability of breast cancer recurrence in the opposite (contralateral) breast in a 64-year-old female with a history of mastectomy for breast cancer on the left, now presenting with asymmetry on a mammogram of the right breast 7 years post-mastectomy, cannot be directly determined from the provided information.
- The annual incidence rate of contralateral breast cancer was reduced from 7.6 per 1,000 patients to 3.9 per 1,000 patients with 5 years of tamoxifen treatment.
- The reduction in incidence of contralateral breast cancer with tamoxifen treatment was 47%. However, the provided information does not include the patient's specific details such as tamoxifen treatment history, and the exact probability of breast cancer recurrence in the opposite breast for this patient cannot be determined 2.
From the Research
Breast Cancer Recurrence in Contralateral Breast
The probability of breast cancer recurrence in the opposite (contralateral) breast in a 64-year-old female with a history of mastectomy for breast cancer on the left, now presenting with asymmetry on a mammogram of the right breast 7 years post-mastectomy, can be assessed based on available evidence.
Asymmetry on Mammogram
- Asymmetry on a mammogram is an area of increased density in one breast when compared to the corresponding area in the opposite breast 3.
- Most asymmetries are benign or caused by summation artifacts, but an asymmetry can indicate breast cancer 3.
- A developing asymmetry, which is new or increased in conspicuity compared to the previous mammogram, should be viewed with suspicion because it is an uncommon manifestation of breast cancer 4.
Probability of Malignancy
- The probability of malignancy in a developing asymmetry is sufficiently high to justify recall and biopsy 5.
- In a study of 281 screening-detected developing asymmetries, 36 cases of cancer were identified, resulting in a positive predictive value (PPV1) of 12.8% and a PPV2 of 42.9% 5.
- Another study found that 19.4% of focal asymmetric densities were malignant, and 2 out of 7 patients with breast cancer had no focal abnormality at sonographic examination 6.
Diagnostic Evaluation
- Diagnostic mammography, sonography, breast magnetic resonance imaging, or biopsy may be required to evaluate an asymmetry 3.
- Targeted ultrasonography (US) should be performed to identify potentially benign causes of the developing asymmetry or identify a target for biopsy 4.
- Lack of a US correlate should not preclude biopsy of a developing asymmetry 4.
Conclusion Not Provided as per Request
However, it is essential to note that the provided evidence does not directly address the probability of breast cancer recurrence in the contralateral breast. The studies primarily focus on the evaluation and management of asymmetries on mammograms. Therefore, the probability of breast cancer recurrence in this specific scenario cannot be accurately determined based on the available evidence.