Familial breast cancer in southern Finland

Abstract

We evaluate the validity of the family history of breast cancer reported by the patient and the number of families and individuals at risk and potentially benefiting from surveillance. Family history of cancer was systematically screened in three different series of breast cancer patients. Breast cancer families were defined by the selection criterion of at least three first- or second-degree relatives with breast or ovarian cancer (including the proband) and their genealogy and cancer diagnoses were confirmed. Family history of breast or ovarian cancer was reported by approximately 30% of the patients and 7–9% were classified as breast cancer families. On average, there were 3.1 healthy female (age: 20–70 years) first degree relatives per family potentially at high risk. Index patients reported 87% of all confirmed diagnoses and the primary site was correct in 93–95% of the reported cases. The incompleteness and errors in accuracy should be considered in epidemiological studies and verification of the diagnoses is important when deciding clinical management.

Introduction

Breast cancer is the most common malignancy affecting women worldwide, and in Finland, approximately 3200 new breast cancer cases are diagnosed annually among 2.6 million women [1]. One of the strongest risk factors for breast cancer is family history 2, 3. Epidemiological studies have shown increased breast cancer incidence in relatives of breast cancer patients compared with the general population, especially if breast cancer has been diagnosed at a young age 4, 5 or if the patient has bilateral disease 5, 6. Genetic models have provided evidence for a rare autosomal dominant gene(s), with susceptibility to breast cancer 7, 8. Elevated risk for ovarian cancer has also been found among relatives of breast cancer patients 9, 10 and a breast/ovarian cancer susceptibility gene(s) is (are) estimated to account for 7% of breast cancer cases and 10% of ovarian cancer cases in the general population [11]. Two major dominantly inherited genes predisposing to breast and ovarian cancer have been identified, BRCA1 and BRCA2 12, 13 with a high risk of early onset breast cancer and varying risk of ovarian cancer [14]. This has also made predictive diagnostic tests of cancer predisposition possible in some families.

However, selection of families to undergo genetic testing is based on the family history recalled by the patient. Furthermore, in many families no causative gene or mutation can be found and risk assessment is based solely on family history. A few study groups have assessed the accuracy of reported family history of breast cancer. It is considered to be quite precise especially among first degree relatives whilst less accurate data are achieved about breast cancer in second degree relatives 15, 16, 17 or about some other cancer sites 15, 16, 17, 18, 19, 20. Furthermore, false family histories have been documented with serious implications for risk assessment and clinical management [21]. Altogether, in the clinical family counselling the correct family history is critical in the risk estimation as well as treatment and follow-up decisions.

We report here the results of systematic screening for family history in three different series of breast cancer patients, and systematic confirmation of family history as well as cancer diagnoses within defined breast cancer families. The impact of these on family counselling and the clinical management of the breast cancer families is discussed.