Breast cancer incidence has risen for at least 70 years. Hormone use has been v ariously linked to the rise and has recently been implicated particularly in the etiology of lobular, as opposed to ductal, invasive cancer but there has been little consideration of the receptor status of the tumors. Data from the files of the Kaiser Permanente Northwest Tumor Registry allowed us to generate a comprehensive report combining clinical, pathological and receptor data from a single source over 44 years. This Registry collects material from several interlinked clinical and laboratory data systems and enrolls all cases of cancer in a defined population, allowing accurate calculation of rates. All tumor specimens are processed by a single laboratory and diagnoses rendered by a small group of pathologists working exclusively for KPNW. Estrogen receptor determinations became common in 1978 (69% of cases) and were done in 94% of cases by 2003. Determinations have always been done in laboratories surveyed and approved by the cooperative groups for clinical trials in breast cancer. Using these KPNW data, we investigated breast cancer incidence patterns as a function of histologic type, estrogen receptor status, and disease stage over a 44-year period. Of the 8543 breast cancers among women diagnosed and treated at KPNW, 1960-2003, 7275 were invasive, 5323 of ductal histology and 774, lobular. Breast cancer incidence has increased overall by 181% from 1960 to 2003 (80.8 to 145.9); all rates are age-adjusted (2000 standard) annual rates per 100,000 women. Incidence did not change for women less than 45 yrs at diagnosis but rose 150% for women 45-59 yrs and 246% for women over 60 yrs. Ductal cancer increased from 73 to 116.2 between 1960 to1999 and has fallen to 104.5 by 2003. Lobular cancer was essentially undiagnosed in 1960 and rose progressively to 10.2 (1979), then 13.0 (1990) and ultimately to 23.0 by 2003. Most strikingly, the rise in incidence of all cancers, irrespective of histology, has been confined to ER+ tumors. Overall, ER+ cancers rose from 32 to 109.9 (344%) in the period between 1978 and 2003. At the same time ER- cancers fell from 37.3 to 16.4 (44%). Receptor-positive ductal cancers, accounting for about 80% of all breast cancers, rose by 302% but ER+ lobular cancers, relatively uncommon in the earliest years, increased by 799% during this time to constitute nearly 20% of all cancers by 2003. The common thread for the increases in incidence appears to be receptor positivity. Indeed, ER- cancers and those among younger women (more likely to be ER-) are stable or declining in incidence over many years. Because the pattern of age-adjusted incidence rate increases for both lobular and ductal carcinoma resembles the increased use of postmenopausal hormones in the U.S. during the same period, this known breast cancer risk factor may explain these phenomena.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]