PGR and breast cancer: This is supported by the observation that the number of hormone receptor–positive BC cases increased from 1992 to 1998 among patients aged 40 to 69 years,23 a pattern that may be caused by hormonal factors, such as early age at menarche, higher body mass index, and increased use of hormone therapy.23,24 Alternatively, tumors that might be detected as ER negative and/or PR negative may have subsequently been classified as ER positive and/or PR positive with the development of immunohistochemical techniques.