1. ¹Translational Oncology Westmead and Nepean Hospitals, Westmead, NSW 2145, Australia
2. ²Westmead Institute for Cancer Research, Westmead Millennium Institute, Westmead, NSW 2145, Australia
3. ³University of Sydney, Camperdown, NSW 2006, Australia
4. ⁴Department of Tissue Pathology, Institute of Clinical Pathology and Medical Research Westmead Hospital, Westmead, NSW 2145, Australia
5. ⁵BreastScreen Greater Western Sydney, Parramatta, NSW 2150, Australia
6. ⁶Division of Medicine, Westmead Hospital, Westmead, NSW 2145, Australia

Correspondence: Dr RL Balleine, Department of Medical Oncology, Westmead Hospital, PO Box 533, Wentworthville, NSW 2145, Australia. E-mail: rosemary_balleine@wmi.usyd.edu.au

⁷Both these authors contributed equally to this work

Revised 1 January 2005; Accepted 8 February 2005; Published online 5 April 2005.

Abstract

Histopathologic features of breast cancer such as tumour size, grade and axillary lymph node (LN) status variably reflect tumour biology and time. Recent evidence suggests that the biological character of breast cancer is established at an early stage and has a major impact on clinical course. The aim of this study was to distinguish the impact of biology on breast cancer histopathology by comparing features of breast cancers diagnosed following population mammographic screening with prevalent vs incident detection and screening interval. Central histopathology review data from 1147 cases of ductal in situ and/or invasive breast cancer were examined. Size, grade and LN status of invasive cancers were positively correlated (P<0.001). Prevalent invasive cancers were larger (P<0.001) and more likely to be LN positive (P=0.02) than incident cases, but grade was not associated with screening episode (P=0.7). Screening interval for incident cancers was positively associated with invasive cancer size (P=0.05) and LN status (P=0.002) but not grade (P=0.1). Together, these data indicate that biology and time both impact on size and LN status of invasive breast cancer, but grade reflects biology alone. In view of the clinical importance of breast cancer biology, grade as its most direct indicator assumes particular significance.