Published July 8, 2024 BREAST CANCER Management of Breast Ductal Carcinoma in Situ Ductal carcinoma in situ (DCIS), which is also referred to as intraductal carcinoma or Stage 0 BC, accounts for approximately 18% to 25% of BC cases in the United States. DCIS is a noninvasive or preinvasive form of BC in which the cells that line the BC ducts are cancerous, but they have not spread through the ducts or into the adjacent breast tissue. About one-quarter to one-half of patients with DCIS will go on to develop invasive BC, making early intervention important.An invited review update was published on the management of DCIS. Depending on the extent of disease, standard treatment of DCIS involves surgical excision, either in the form of breast-conserving surgery (BCS) or a total mastectomy. If BCS is performed, it is also advised that patients undergo adjuvant radiotherapy and a 5-year course of endocrine therapy (ET) if the tumor is estrogen receptor–positive (ER+). This is coupled with enhanced surveillance, including an annual mammogram and physical examination every 6 to 12 months during the first 5 years postdiagnosis.The update discusses the various imaging options in addition to mammography, trials that have replaced surgery with aggressive surveillance, risk stratification after surgical excision, radiation therapy, systemic therapies including ET, and vaccines in development. On mammography, DCIS appears as microcalcifications. Additional imaging options include the use of MRI, which can detect focal (<5 mm) masses or nonmass enhancements. The use of MRI has been associated with an 8% false-positive rate for DCIS and invasive BCs, as well as detection of noncalcified DCIS, which is associated with lesions that are less likely to progress to invasive BC. Contrast-enhanced mammography (CEM) is another imaging technique that involves the use of IV iodinated contrast media to identify neovascularity related to BC tumors. It is associated with improved DCIS detection rates compared with standard mammography; however, it has not widely been incorporated into clinical practice.While there is interest in omitting or deescalating surgical interventions in DCIS, trials in this area are ongoing and such practices are not recommended at this time.There is also debate about the methods used to classify patients as low risk of progression to invasive disease. Tools have been developed to help with risk stratification, but they need to be validated in well-done clinical trials.Radiation therapy (RT) in BC has been associated with an increased risk of cardiovascular disease in patients with left-sided BC and the development of radiation-associated angiosarcoma in one per 1,000 BC patients treated with RT. Different RT modalities include the use of conventional RT, hypofractionated whole breast RT, and boost RT. The use of the various RT methods is dependent upon accurate risk stratification.The two pharmacologic therapeutic interventions discussed in this review include the use of ET for women with ER+ DCIS and the status of vaccines to prevent the development of invasive BC. This article states that for women with ER+ DCIS who have undergone BCS, adjuvant therapy with 5 years of tamoxifen therapy is typically prescribed. Ten-year follow-up data on the use of tamoxifen 5 mg orally daily for 3 years in women with intraepithelial neoplasia (including DCIS) who underwent BCS with/out RT demonstrated a 50% decrease in the risk of recurrence of DCIS. DCIS was present in 70% of the overall study population. Aromatase inhibitors (AIs) have also demonstrated benefit in high-risk postmenopausal women. A 12-year follow-up study on the use of anastrozole 1 mg orally daily for 5 years in high-risk postmenopausal women (i.e., high-risk consisted of risk of developing BC that was at least two to up to four times higher than age-matched controls) found a 59% reduction in the incidence rates of BC. The use of preoperative ET therapy is currently under investigation.Also under investigation is the development of a vaccine to treat DCIS. The most common vaccines being studied include a human epidermal growth factor receptor 2 (HER2) pulsed dendritic cell vaccine that restores the T-helper type 1 cell responses that are downregulated in HER2-positive tumors and a Nelipepimus-S peptide vaccine, which promotes a cytotoxic T-lymphocyte response. The National Comprehensive Cancer Network (NCCN) provides guidance on the management of DCIS. NCCN recommends the use of ET for 5 years for patients with ER+ DCIS if the patient has been treated with BCS and RT (Category 1 recommendation) or with excision alone. The NCCN advises the use of tamoxifen 20 mg/day for 5 years but states that low-dose tamoxifen (5 mg/day or 10 mg/every other day for 3 years) is acceptable in patients who are symptomatic or who are unwilling to take the standard 20-mg daily oral dose. Tamoxifen or an AI are recommended for postmenopausal women, with the latter drug class recommended in patients aged <60 years or those with concerns for thromboembolism. Studies have stressed the importance of adherence to ET in DCIS to minimize the development of subsequent BC tumors.Given the widespread prevalence of DCIS, pharmacists should be aware of how to manage patients with this condition. They should play an active role in patient education stressing the need for adherence, and they should counsel on the risk and management of adverse drug events associated with preventative therapies.The content contained in this article is for informational purposes only. The content is not intended to be a substitute for professional advice. Reliance on any information provided in this article is solely at your own risk.