The following article features coverage from the American Society of Clinical Oncology 2020 meeting. Click here to read more of Cancer Therapy Advisor‘s conference coverage.

The absolute 8-year risk of ipsilateral invasive breast cancer (iIBC) in women with non-high grade ductal carcinoma in situ (DCIS) who underwent surveillance without surgical intervention within 6 months of diagnosis was less than 10%, according to a retrospective study presented during the ASCO20 Virtual Scientific Program.

While the standard-of-care for most patients diagnosed with ductal carcinoma in situ (DCIS) is surgical resection, data regarding the natural history of DCIS in patients who do not undergo locoregional treatment are limited. Hence, questions remain as to whether current approaches to the management of DCIS result in the overtreatment of a significant percentage of patients.

Researchers conducted an analysis using a random sample of women with DCIS detected on breast cancer screening and confirmed by biopsy from over 1000 Commission on Cancer–accredited facilities between 2008 and 2014. When patients were stratified according to treatment received and to exclude those who underwent mastectomy within 6 months of diagnosis of DCIS, 14,245 were treated with breast-conserving therapy (BCS) as DCIS-related index surgery with or without radiation therapy within 6 months of diagnosis and 1914 patients were treated with surveillance alone (SV).

Demographic and clinicopathologic data, including subsequent breast events in the 10 years following a diagnosis of DCIS, were abstracted from medical records. Propensity score modeling with inverse probability weighting were used to account for  potential confounding factors as a means of adjusting for treatment selection bias. The primary outcome measure was the 8-year absolute difference in iIBC risk between the BCS and SV subgroups.


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Median patient age was 61 years, the percentages of patients identifying as Caucasian and those with estrogen receptor-positive disease were 80% and 82%, respectively. Nuclear grade I/II (ie, low-grade) DCIS was diagnosed in 54.5% of patients. The percentage of patients with a Charlson comorbidity score of at least 2 was significantly higher in the SV group (14.2%) compared with the BCS group (6.4%; P <.001).

A comparison of 8-year iIBC risk in the 2 treatment-based groups revealed an absolute difference of 4.7% (BCS, 3.0% vs SV, 7.7%; log rank P <.0001). When a subgroup analysis was performed that included only those patients aged at least 60 years with non-high grade DCIS, the absolute difference in 8-year risk of iIBC was reduced to approximately 3%, whereas it was 7%-8% in those with disease characterized by high-grade and estrogen receptor negativity.

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Eight-year disease-specific survival was 99.77% and 97.37% for the overall group of patients treated with BCS or SV, respectively (log rank P <.001).

The study authors stated that this result may “be due to persistent differences in unmeasured covariates between groups after balancing.” However, they also noted that breast cancer-specific mortality may be higher in the SV group.

The results of this study “emphasize the importance of ongoing active monitoring (COMET, LORD, LORIS, LORETTA) that seek to determine whether active surveillance may be a viable alternative to immediate surgery for low-risk DCIS patients,” the researchers added.

Read more of Cancer Therapy Advisor‘s coverage of the ASCO 2020 meeting by visiting the conference page.

Reference

Ryser MD, Hendrix L, Thomas SM, et al. Ipsilateral invasive cancer risk after diagnosis with ductal carcinoma in situ (DCIS): Comparison of patients with and without index surgery. Presented at: ASCO20 Virtual Scientific Program. J Clin Oncol. 2020;38(suppl):abstr 519.