Abstract P1-22-01: Predictors of inaccurate pre-operative size assessment of screen detected DCIS and impact on recurrence rates
Authors: Kirwan Cliona Clare , Hilton Bridget , Clements Karen , Stobart Hilary , Wallis Matthew , Mylvaganam Senthurun , Provenzano Elena , Maxwell Anthony , Sharma Nisha , Shaaban Abeer , Dodwell David , Dulson-Cox Joanne , Sawyer Elinor , Kearins Olive , Brace-McDonnell Samantha , Pinder Sarah , Thompson Alastair M 
Published: March 2022

Background: Disparity between mammographic and pathological sizing of DCIS can lead to surgical overtreatment, with poor cosmetic outcomes of breast conservation surgery (BCS) or inappropriate mastectomy versus undertreatment, with subsequent need for re-excision. In addition, where mammographic size is smaller than pathological size, this may reflect an increased risk of mammographically occult residual disease post surgery; where pathological size is smaller than mammographic size there is a possibility of pathological underestimation or missed positive margins, with both scenarios resulting in increased risk of recurrence. Methods: The Sloane Project, within the UK NHS Breast Screening Programme, is a prospective cohort study of screen detected DCIS (2003-2012), with recurrence data for a median follow-up of 9 years. The NHS Breast Screening Programme screens women from age 50-70. We assessed factors associated with mammographic/pathology disparity, leading to i) 'downsizing' from pre-operative mammographic size estimation to final surgically resected pathological size or ii) 'upsizing' from pre-operative mammographic size to surgically resected pathological size. We defined 'downsizing' as pathological size &lt;10mm or &lt;5mm (largest diameter) smaller than mammographic size and 'upsizing' as pathological size &gt;10mm or &gt;5mm larger than mammographic size. Ipsilateral recurrence rates were determined in patients with mammographic/pathology disparity (downsized or upsized) compared to those with accurate preoperative sizing. Results: Using a 10mm size disparity, among 10829 patients, DCIS was downsized (pathological size smaller than mammographic size) in 26%, upsized in 19% and similar in 54%. Mastectomy was associated with marked mammographic/pathology disparity, with a 3.90RR of downsizing (p&lt;0.0001, 95% C.I 3.52,4.31) and a 4.72RR of upsizing (p&lt;0.0001,95% C.I 4.23, 5.27). Presence of microcalcification was associated with mammographic/pathology disparity, yielding a 1.29 RR of downsizing (p=0.0034, 95% C.I. 1.09,1.54) and 1.53 RR of upsizing (p&lt;0.0001, 95% C.I. 1.25,1.88). Casting or linear calcification (compared to granular or punctate) was associated with a 2-fold RR of downsizing. For each 1mm increase in mammographic size, the relative risk (RR) of downsizing increased by 1.07 times (p&lt;0.0001, 95% CI 1.073,1.080). A 1.01 RR of downsizing for every 1 year younger (p=0.0002, 95% CI 1.01,1.02), contrasted with a 1.44 RR of upsizing with high mammographic density.

The results remained similar when patients prescribed endocrine therapy or radiotherapy were excluded. Re-excision (but not completion mastectomy) is associated with increased recurrence, with recurrence occurring in 237 of 5157 not requiring re-excision but 99 of 1488 requiring re-excision; RR: 1.45 (1.15-1.82). Conclusion: Large mammographic size, microcalcification casting features and young age (size overestimation) versus microcalcification and high density (size underestimation) should be considered in selecting surgery for DCIS. Mammographic/pathology disparity of only 5mm, whether this leads to downsizing or upsizing, is associated with an increased risk of ipsilateral recurrence after breast conservation.

Table 1.In patients undergoing breast conservation, impact of 10mm and 5 mm mammographic/pathology disparity on ipsilateral recurrence rateTotalIpsilateral recurrence, n (%)RR (CI)Change in size of &gt;10mmNo change3062158 (5.2%)1downsized111666 (5.9%)1.15 (0.87-1.51)upsized52036 (6.9%)1.34 (0.95-1.90)unknown19112 (6.3%)1.22 (0.69-2.15)TOTAL4889272 (5.6%)Change in size of &gt;5mmNo change2783118 (4.2%)1downsized1953115 (5.9%)1.39 (1.08-1.78)upsized139580 (5.7%)1.35 (1.03-1.78)unknown23814 (5.9%)1.39 (0.81-2.38)TOTAL6369327 (5.1%)

Citation Format: Cliona Clare Kirwan, Bridget Hilton, Karen Clements, Hilary Stobart, Matthew Wallis, Senthurun Mylvaganam, Elena Provenzano, Anthony Maxwell, Nisha Sharma, Abeer Shaaban, David Dodwell, Joanne Dulson-Cox, Elinor Sawyer, Olive Kearins, Samantha Brace-McDonnell, Sarah Pinder, Alastair M Thompson. Predictors of inaccurate pre-operative size assessment of screen detected DCIS and impact on recurrence rates [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-22-01.