Introduction
Knowledge of tumor growth is important in the planning and evaluation of screening programs, clinical trials, and epidemiological studies. Studies of tumor growth rates in humans are usually based on small and selected samples. In the present study based on the Norwegian Breast Cancer Screening Program, tumor growth was estimated from a large population using a new estimating procedure/model.

Methods
A likelihood based estimating procedure was used, where both tumor growth and screen test sensitivity [STS] were modeled as continuously increasing functions of tumor size. The method was applied to cancer incidence and tumor measurement data from 395 188 women aged 50-69 years.

Results

Tumor growth varied considerably between subjects, with 5 % of tumors using less than 1.2 months to grow from 10 to 20 mm in diameter, and another 5 % using more than 6.3 years.

The mean time a tumor needed to grow from 10 to 20 mm in diameter was estimated to 1.7 years, increasing with age. STS was estimated to increase sharply with tumor size, going from 26 % at 5 mm to 91 % at 10 mm. Compared to previously used Markov models for tumor progression, the applied model gave considerably higher model fit (85 % increased predictive power) and provided estimates directly linked to tumor size.

Conclusion

Screening data with tumor measurements can provide populationbased estimates of tumor growth and STS directly linked to tumor size. There is a large variation in breast cancer tumor growth, with faster growth among younger women.

Harald Weedon-Fekjær, Bo H Lindqvist, Lars J Vatten, Odd O Aalen and Steinar Tretli

Breast Cancer Research 2008, 10:R41doi:10.1186/bcr2092
Published: 8 May 2008