Abstract PD3-04: Classic lobular carcinoma in situ in the Netherlands: A population-based analysis

• Published in: Cancer research (Chicago, Ill.) Ill.), 2020-02, Vol.80 (4_Supplement), p.PD3-04-PD3-04
• Main Authors: van Maaren, Marissa Corine, Avila, Agustin Ortega, Bart, Jos, Westenend, Pieter J, Siesling, Sabine
• Format: Article
• Language: English
• ISSN: 0008-5472; 1538-7445
• DOI: 10.1158/1538-7445.SABCS19-PD3-04

Background: Lobular carcinoma in situ (LCIS) is a non-invasive proliferation of epithelial cells of the terminal-duct lobular unit. Although LCIS is non-invasive itself, studies in the past showed that patients with LCIS have a 4-12 times higher risk of developing invasive breast cancer than the general population. Therefore, the optimal management of LCIS is still subject of debate. Despite lack of information about LCIS in the Dutch population, the Dutch guidelines recommend active surveillance for classic LCIS. This study aims to describe incidence and management of classic LCIS over time in the Netherlands, and to understand its behavior in terms of survival and the risk of developing subsequent ductal carcinoma in situ (DCIS) or invasive breast cancer. Methods: All female patients diagnosed with classic LCIS between 1989-2017 in the Netherlands were identified from the nationwide population-based Netherlands Cancer Registry. Patients previously diagnosed with DCIS or invasive breast cancer were excluded. Standardized incidence ratios (SIR) were calculated to estimate the risk of subsequent DCIS and invasive breast cancer, using data on population size from Statistics Netherlands (CBS). Multivariable Cox proportional hazards regression was performed to estimate hazard ratios (HR) of overall mortality and risk of subsequent invasive breast cancer for different patient-, tumor- and treatment-related characteristics. Competing risks were taken into account. Relative survival was estimated using the Ederer II method, with expected mortality of the general population (matched by age, gender, calendar year) as a reference. Results: We included 1,890 patients. The median age at diagnosis was 51 years (range 24-91 years). The incidence of classic LCIS increased from 186 patients between 1989-1993 to 497 patients between 2014-2017. Of all patients, 50.5% were treated with breast-conserving surgery, 10.2% were treated with mastectomy, 12.6% were treated with an unknown type of surgery and 26.7% did not receive surgery. While in 1989 all patients were surgically treated, only 41% were surgically treated in 2017. Radiotherapy was administered in 3.1% and endocrine therapy in 0.2% of the patients. Median follow-up to death, and subsequent DCIS or invasive breast cancer was 8.5 years (range 0-29 years) and 6.9 years (range 0-27 years). Unadjusted 10- and 20-year overall survival rates were 91% (95%CI:90-93%) and 76% (95%CI:73-79%). Unadjusted 10- and 20-year relativ