Abstract PS4-23: An analysis of the clinical and economic impact of the 21-gene recurrence score (RS) in invasive lobular early-stage breast cancer (ESBC) in Ireland (2021)

Abstract Background: The use of the 21-gene recurrence score assay (RS) has reduced chemotherapy (CT) administration in patients with hormone receptor (HR)-positive, HER-2 negative, lymph-node negative, early stage breast cancer (ESBC). Invasive lobular carcinoma (ILC) accounts for up to 15% of all breast cancers. This study uses real world data to assess (1) the effect of RS testing on treatment decision making in patients with ILC and (2) the economic benefit of testing in this subgroup. Methods: From October 2011 to February 2019, a retrospective, cross-sectional, observational study was conducted on HR+, HER-2 negative, lymph-node negative, ESBC patients with ILC who had RS testing in Ireland. For the decision impact analysis, a survey of Irish breast medical oncologists presumed that, without RS testing, CT would be recommended to patients with histological grade (G) 2 and 3 tumours and not for G1 tumours. In accordance with TAILOR-x results, patients were classified overall as low risk (RS≤25) and high risk (RS&amp;gt;25) and patients ≤50 years old were low risk (RS 0-15), intermediate risk (RS 16-25), and high risk (RS&amp;gt;25). Data were collected from electronic patient records. Descriptive statistics were used. Cost data were obtained from the National Healthcare Pricing Regulatory Authority. The economic analysis was adjusted for changing treatment and assay costs over the study period. Results: 166 patients with ILC were identified. Mean age was 59 years. Mean tumour size was 2.3cm (range 0.7-5.8). The majority had G2 tumors (n=152, 92%) with a small number of G3 (n=7, 4%) and G1 (n=7,4%). Overall, 153 patients (92.2%) had a low RS (≤25), 12 (7.2%) had high RS (&amp;gt;25), and 1(0.6%) was unknown. All 12 patients with RS&amp;gt;25 had G2 tumours, 6/12 (50%) had tumour size &amp;gt;3cm, 4(33.3%) were PR+ and 8(66.7%) were PR negative. In 29/166 (17.5%) patients, aged ≤50 at diagnosis, RS was ≤15 in 16(55%), 16-20 in 6(21%), 21-25 in 5(17%), &amp;gt;25 in 1(3.5%) and unknown in 1(3.5%). The majority of these patients (27, 93%) had G2 tumours, 1 had G1 and 1 had G3. Post RS testing 124 patients (74.5%) had a change in CT recommendation; all from CT to hormone therapy. In total, only 35 patients (21%) received CT. In this group, RS was 0-15 in 3(9%), RS 16-25 in 19(54%), RS &amp;gt;25 in 12 (34%) and unknown in 1(3%). Eight of 35 patients (23%) were aged ≤50. The most common CT regimen administered was docetaxel plus cyclophosphamide (TC). RS testing achieved a 78% reduction in chemotherapy use. This resulted in savings of €900,000 in treatment costs. With the incorporation of the assay cost, the net savings totalled approximately €400,000. Conclusions: Ireland was the first public health care system to reimburse the 21-gene recurrence score assay in Europe. There is limited evidence demonstrating the benefits of RS in ILC. In our study, the use of the test has resulted in a 78% reduction in chemotherapy use in an Irish ILC patient population and a substantial cost saving (greater than €400,000) to the Irish Healthcare System. Citation Format: Mehala Tharmabala, Lynda McSorley, Fathiya Al Rahbi, Evoy Denis, James G Geraghty, Rothwell Jane, Damian McCartan, Enda McDermott, Maccon M Keane, John Kennedy, Seamus O'Reilly, Steve Millen, John Crown, Lilian Mary Smyth, Catherine Margaret Kelly, Prichard Ruth, Cecily Quinn, Janice M Walshe. An analysis of the clinical and economic impact of the 21-gene recurrence score (RS) in invasive lobular early-stage breast cancer (ESBC) in Ireland [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS4-23.