Breast cancers found by screening: earlier detection, lower malignant potential or both?

Area of Science:

• Oncology
• Public Health
• Diagnostic Imaging

Background:

• Breast cancer screening programs aim for early detection.
• Understanding differences between screen-detected and clinically detected cancers is crucial for evaluating screening effectiveness.
• Previous studies suggest potential differences in tumor biology or stage at detection.

Purpose of the Study:

• To compare the characteristics of clinically detected versus screen-detected invasive breast cancers.
• To determine if observed differences are due to earlier diagnosis or distinct tumor biology.
• To stratify comparisons by tumor size to elucidate these differences.

Main Methods:

• Population-based study using data from the Eindhoven Cancer Registry (1996-1999).
• Analysis of 568 screen-detected and 630 clinically detected invasive breast cancers.
• Stratified comparisons based on tumor size (<=1.0 cm, 1.1-2.0 cm, 2.1-3.0 cm).

Main Results:

• Screen-detected cancers were smaller, had negative lymph nodes, positive estrogen/progesterone receptor status, and lower mitotic activity.
• Differences were most pronounced in smaller tumors (< or = 1.0 cm and 1.1-2.0 cm).
• No significant differences were found for tumors 2.1-3.0 cm; adjustments for tumor size diminished most observed differences.

Conclusions:

• Screen-detected breast cancers represent tumors in an earlier developmental phase, not a biologically distinct group.
• The findings suggest that breast cancer screening programs facilitate earlier diagnosis.
• Adjusting for tumor size is essential when comparing screen-detected and clinically detected cancers.