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12 December 2018

The San Antonio Breast Cancer Symposium is the largest medical conference devoted to breast cancer. Held every year in San Antonio, TX, it attracts a large international audience and there are often practice-changing studies. While I was not able to attend the meeting in person, I’ve provided just a few of the studies that caught my attention. This is by no means a comprehensive post – the meeting is enormous – but I have also included several summary links below with additional information.

Her2/neu Positive Breast Cancer
The KATHERINE study assessed patients treated with chemotherapy and trastuzumab (Herceptin) prior to surgery. Patients who had residual disease at surgery (meaning the chemotherapy did not kill all of the cancer) were then treated either with trastuzumab (standard of care is to complete 52 weeks of therapy) or trastuzumab-emtansine (T-DM1, Kadcyla). The study found that after 3 years of follow up, patients treated postoperatively with trastuzumab emtansine had a 50% lower risk of developing recurrence of invasive breast cancer (12.2% versus 22.2%). The findings were published on the day of presentation in the New England Journal of Medicine.

Adverse events were more common in the trastuzumab-emtansine arm (98% versus 93%). 25.7% had grade 3 or higher adverse events in the trastuzumab-emtansine arm compared to 15.4% in the trastuzumab arm. While based on these results, there is some anticipation of FDA approval, cost of the medication and insurance coverage are significant concerns.

Relationship Between pCR and Outcomes
Patients who receive neoadjuvant (prior to surgery) chemotherapy and are found to have no residual tumor (pathologic complete response – pCR) at the time of surgery, had improvements in recurrence and survival rates. The meta-analysis showed that approximately 21% of treated patients had a pCR, which was more likely if the tumor was triple negative or Her2/neu positive. The event-free survival rate was 88% in patients who had a pCR versus 67% for those with residual disease. The authors noted that in patients who had a pCR, additional chemotherapy after surgery may not be necessary. In addition, they suggested that in whose  who had residual cancer, additional chemotherapy (see the KATHERINE study above) could be considered.
ASCO Post on pCR Meta-Analysis

Tamoxifen for DCIS, LCIS and ADH
Tamoxifen is often used to help reduce the risk of developing invasive breast cancer in patients who are at high risk, including those with ductal carcinoma in-situ (DCIS), lobular carcinoma in-situ (LCIS) and atypical ductal hyperplasia (ADH). The standard dose of tamoxifen is 20mg daily. Hot flashes and sleep disturbance impact some patients who take tamoxifen, and the medication is also associated with a risk of developing blood clots and endometrial cancer. These potential side effects keep some women from even starting the medication. In addition, studies note that approximately 25-30% of breast cancer patients treated with endocrine therapy stop treatment due to side effects.

The TAM-01 study compared a low dose of tamoxifen (5mg per day) to placebo in patients with DCIS, LCIS and ALH. 500 patients were randomized and treated for 3 years. After median follow up of 5 years, 5.5% of patients in the low dose tamoxifen arm and 11.3% of patients in the placebo arm had recurrence or development of new disease, suggesting a risk reduction of approximately 50%. This is what is also seen from the standard, 20mg dose. Side effects were similar in the 2 groups.

The findings suggest that a very low dose, 3 year (current standard is 5 years for risk reduction) of tamoxifen may be sufficient in these patients who are on the medication for risk reduction. Unfortunately, the results cannot be extrapolated to patients who are on tamoxifen as part of treatment for invasive breast cancer. It was also noted in some of the commentary that tamoxifen is not commercially available in 5mg doses, but patients may consider taking 10mg every other day.
ASCO Post on TAM-01

Genetic Testing
Genetic testing in patients diagnosed with breast cancer is based on age at diagnosis and family history of breast, ovarian and other cancers. A study presented and simultaneously published in the Journal of Clinical Oncology noted that approximately 50% of patients with a pathogenic or likely pathogenic mutation were missed by current testing guidelines. Of patients who did not meet current guidelines for genetic testing, 7.9% were found to have a pathogenic or likely pathogenic mutation. The authors recommended panel genetic testing for all newly diagnosed breast cancer patients, which certainly could impact treatment recommendations surveillance and treatment recommendations for family members.

Hot Flashes
Oxybutynin (Ditropan and others) is a medication commonly used for urinary incontinence. It was compared to placebo in a double-blinded study, to assess impact on menopausal symptoms in women being treated for breast cancer with tamoxifen or aromatase inhibitors. The study showed that patients taking oxybutynin had decreased hot flash scores and also reported improvements in sleep and quality of life.
ASCO Post interview with Dr. Leon-Ferre

Radiation Therapy after Lumpectomy
The long-awaited results of NSABP B-39 were presented by Dr. Frank Vicini. There are several ways to deliver radiation therapy after lumpectomy – traditional whole-breast irradiation and various forms of partial breast irradiation (external- and catheter-based). The study noted that after 10 years of follow up, local (in-breast) recurrence rates were low in all groups, approximately 4%. Patients treated with partial breast irradiation had a slightly higher (<1%) rate of in-breast recurrence. This study is important for 2 reasons:
– Local recurrence rates were very low, approximately 4%. We have traditionally quoted (based on older studies) a local recurrence rate of approximately 10% after lumpectomy and radiation. This current study notes that local recurrence rates after lumpectomy and radiation are very close to that of mastectomy (1-5%).
– Partial breast irradiation is a reasonable option for selected patients. There was a small (but statistically significant) increase in local recurrence compared to whole breast radiation. Whether that difference is important for an individual patient or not is something that should be discussed with her treatment team. The study noted no difference I overall survival. Grade 3 and 4-5 toxicities were slightly higher in the patients who received partial breast irradiation compared to whole breast irradiation (9.6% versus 7.1% grade 3 and 0.5% versus 0.3% grade 4-5).

It is important to note that at the time of study accrual, whole breast irradiation was given over the course of approximately 6 weeks. Current practice is to utilized a “hypofractionated” protocol, which treats in about 3 – 3 ½ weeks.  

Breast Surgery Choice and Quality of Life
A study assessing long-term quality of life in young patients with breast cancer found that those who underwent unilateral or bilateral mastectomy had lower breast satisfaction and sexual / psychosocial well-being scores compared to those who underwent breast conserving surgery. 561 patients were enrolled with a median age at diagnosis of 37. 28% underwent breast conserving surgery, and 72% underwent mastectomy. 72% of the mastectomy patients had a bilateral procedure. Assessments were performed using the BREAST-Q questionnaire, which is a validated survey tool. Patients were surveyed a median of 5.8 years after treatment.

While the results were presented in abstract (not full peer-reviewed manuscript) form, it is still important to consider this information either as a physician counseling a patient on her options or as a patient deciding on her treatment options.
ASCO Post interview with Dr. Dominici

Other Resources:
SABCS Abstracts
ASCO Post Symposium Updates

AACR Blog
Oncology Times – Dr. George Sledge
OncLive Podcast

This post has not been endorsed by the San Antonio Breast Cancer Symposium