Abstract P5-03-01: Breast cancer biology varies dramatically by method of detection and may account for overdiagnosis
Authors: Hayse Brandon , Kanumuri Prathima , Killelea Brigid K , Horowitz Nina R , Chagpar Anees B , Lannin Donald R 
Published: May 2015

Abstract
Background: Epidemiological and clinical trial data suggest that 20%-30% of breast cancers diagnosed by screening represent overdiagnosis; that is cancers that, if left untreated, would never present symptomatically nor cause any harm to the patient later in life. The biology and presentation of these overdiagnosed cancers, however, is not well understood.
Methods: A retrospective review was performed of a prospectively collected database of breast cancers diagnosed at a tertiary academic medical center from 2004-2013. The mode of initial presentation was categorized into five separate groups according to the abnormality that first precipitated a breast workup: screening mammogram, screening MRI, screening ultrasound, self-detected masses, and physician detected masses. The relationship between tumor characteristics and mode of initial presentation was evaluated using bivariate analysis and multivariate logistic regression.
Results: The table shows data for a total of 2,714 cases. As expected, screen-detected cancers were significantly smaller than cancers found by the patient or the physician, and included a higher percent of T1 cancers, whereas palpable cancers had a larger percent of T2 and T3 cancers (p&lt; 0.001). Also not surprisingly, screening modalities detected a higher rate of DCIS compared to symptomatic presentation (p &lt; 0.001). However in addition to a simple stage shift, screen-detected cancers also had a higher proportion of luminal and low-grade cancers, whereas symptomatic cancers had a higher incidence of high-grade and triple-negative cancers (p &lt; 0.001 for each). In a multivariate logistic regression model adjusted for age, race, and tumor size, cancers detected by screening had a lower odds of being triple-negative (OR 0.51, 95% CI 0.35-0.75), and a lower odds of being high-grade (OR 0.43, 95% CI 0.29-0.64) compared to cancers found by the patient.
Conclusion: In addition to a stage shift, screening detects cancers with a much more indolent biology and this may account for the observed rate of overdiagnosis. With the increasing use of MRI and ultrasound for screening, the rate of overdiagnosis is likely to increase further.
Tumor Characteristics by Method of Detection Screening mammogramScreening MRIScreening ultrasoundSelf-detected massPhysician physical examp valueIN SITU % DCIS33% (556/1669)36% (36/101)13% (6/46)4% (33/786)4% (5/112)&lt;0.001INVASIVE Molecular type &lt;0.001ER/PR+, Her2-79% (718/907)85% (45/53)85% (33/39)61% (393/641)75% (63/84) ER/PR+, Her2+7% (63/907)2% (1/53)5% (2/39)11% (67/641)7% (6/84) ER/PR-, Her2+5% (43/907)4% (2/53)06% (40/641)6% (5/84) ER/PR-, Her2-9% (83/907)9% (5/53)10% (4/39)22% (141/641)12% (10/84) Grade &lt;0.001128% (280/983)45% (25/56)42% (15/36)12% (73/633)20% (17/87) 253% (517/983)46% (26/56)42% (15/36)49% (313/633)49% (43/87) 319% (186/983)9% (5/56)16% (6/36)39% (247/633)31% (27/87) Tumor size &lt;0.001T178% (874/1113)81% (53/65)77% (31/40)38% (284/753)49% (52/107) T218% (205/1113)14% (9/65)20% (8/40)47% (354/753)41% (44/107) T33% (30/1113)5% (3/65)3% (1/40)12% (89/753)6% (6/107) T41% (4/1113)003% (26/753)5% (5/107)
Citation Format: Brandon Hayse, Prathima Kanumuri, Brigid K Killelea, Nina R Horowitz, Anees B Chagpar, Donald R Lannin. Breast cancer biology varies dramatically by method of detection and may account for overdiagnosis [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-03-01.