Background
The Prospective Study of Outcome in Sporadic versus Hereditary Breast Cancer (POSH) first started recruiting in June 2001 and will stop recruiting in December 2007. Follow-up is funded until December 2009. There are 2,665 participants recruited to the study by 10 October 2007. All participants were diagnosed with a first primary invasive breast cancer since January 2000 and were ≤ 40 years old at diagnosis. Eligibility criteria also allow inclusion of those with known BRCA gene diagnosed at ≤ 50 years of age.