Protective effects of surgery plus radiotherapy in DCIS wear off with time

30 Dec 2020

At the 12th European Breast Cancer Conference, the results of a major study conducted on women diagnosed with ductal carcinoma in situ (DCIS) were presented and revealed that patients treated with breast conserving surgery (BCS) plus radiotherapy (RT) received a better protection from developing subsequent in situ or invasive lesion than those who underwent BCS alone.1 Nevertheless, the protection was finite as the benefit diminished with time according to the findings of a 10-year assessment.1 The results may serve to remind both the physicians and patients to remain vigilant on continuous disease monitoring and intervention in the long run.

DCIS is a pre-cancerous and non-invasive malignancy confined within the ductal basement membrane of the breast.2,3 Traditional intervention strategies consist of performing mastectomy or BCS supplemented with RT.4 In 2018, there were 669 new cases of DCIS diagnosed in Hong Kong, representing approximately 12.6% of all types of breast cancer cases.5 Despite its comparatively low incidence when compared to the United States, DCIS remains a challenge for the physicians in Hong Kong due to its relatively indolent state that could lead to possible overtreatment if misdiagnosed as invasive.4 There has been controversy revolving around the practice of whether to treat for more or less.2

Dr. Maartje van Seijen, one of the investigators of the DCIS study, shared her concerns in the long-term treatment strategies, “Most women who are diagnosed with DCIS are offered surgery to remove the abnormal breast tissue and they are often also offered radiotherapy, even though the majority would not go on to develop invasive breast cancer. We wanted to look at how this group of women get on in the long term, according to which treatment they received.” The study comprised of more than 10,000 women from the Netherlands who were diagnosed of DCIS between 1989 and 2004.1 They were given either mastectomy, BCS alone, or BCS in combination with RT to evaluate how well these options could prevent subsequent ipsilateral in situ (iDCIS) and/or invasive breast (iBC) lesions, and death.1

During the first 5 years of assessment, when compared to patients who underwent both BCS and RT, those receiving BCS alone were at a higher risk of developing subsequent iDCIS (HR=3.3; 95% CI: 2.5-4.2) and iBC (HR=4.1; 95% CI: 3.0-5.7).1

However, during the 5-10 year assessment, patients with BCS only showed an apparent reduction in the risk of developing iDCIS (HR=2.2; 95% CI: 1.5-3.3) and iBC (HR=2.0; 95% CI: 1.6-2.6) when compared to patients receiving BCS plus RT.1

After 10 years of follow-up, the risk difference between BCS alone and the combination of BCS plus RT further minimized in the development of iDCIS (HR=0.7; 95% CI: 0.3-1.3) and iBC (HR=1.1; 95% CI: 0.9-1.4).1 The overall risk of developing both events, i.e. iDCIS and iBC, was almost the same (HR=1.0; 95% CI: 0.8-1.3) between the two treatment approaches.1

Dr. van Seijen thus concluded, “The risk of DCIS or invasive cancer recurring in these women will diminish over time, whether they had just the breast-sparing surgery or breast-sparing surgery with radiotherapy. This study shows that, overall, the addition of radiotherapy gives women the best chances.” Despite the risk difference narrowing down with time, Dr. van Seijen remarked, “There remains a chance of a new DCIS or invasive cancer developing that is not related to the initial diagnosis and we would expect this risk to be similar between the two types of treatment. In a very small number of women, radiotherapy itself might cause a new breast cancer, often many years after the radiotherapy was given.” In view of their long-term consequences, patients could still consider the third option, mastectomy, which after all carried the lowest risk of progressing to iBC by the end of the study when compared with BCS plus RT (HR= 0.1; 95% CI: 0.1-0.2).1 Nevertheless, mastectomy may not be necessary for all the patients, and Dr. van Seijen reminded that, “Although patients who have a mastectomy have the lowest risk of recurrence, it’s important to remember that, according to previous research, overall survival in patients who have a mastectomy is the same as in patients who have less aggressive treatments. For the majority of women with DCIS, whose condition will never become invasive, mastectomy would be considered over treatment.”

Based on this study, physicians should understand the values and outcomes of different treatment approaches for DCIS and better inform their patients to discuss the best treatment options available.

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