. 2009 Oct 13;27(32):5308–5311. doi: 10.1200/JCO.2009.22.9450

Table 1.

Qualitative Age Interactions

Parameter	Sample Size	RR_{before crossover age in years}
Epidemiologic risk factor
Parity v nulliparity⁷	577 cases, 826 controls	RR_{before 30-44} > 1.0
Obese v lean BMI⁸	Review	RR_{before 50}< 1.0
Black v white incidence rates⁹	440,653 cases	RR_{before 40}> 1.0
Tumor characteristic
Poor v good prognostic factors¹⁰	242,549 cases	RR_{before 50} > 1.0
Breast cancer outcome³⁸	1,398	RR _{before 35} > 1.0
Clinical trial results
Adjuvant Rx for ER+ tumors⁴	7,631 cases	RR_{before 35} > 1.0
Neoadjuvant Rx (NSABP B18)⁵	763 preoperative AC, 760 postoperative AC	RR_{before 50} < 1.0
Chemoprevention (fenretinide)⁶	1,432 cases, 1,435 controls	RR_{before 51}< 1.0

NOTE. Qualitative age interactions are expressed as RRs where one characteristic is compared with a referent characteristic with an assigned RR of 1.0. RR > 1.0 shows increased breast cancer risk or harmful effect while RR < 1.0 shows reduced breast cancer risk or protection compared with the referent characteristic. The crossover age reflects the approximate age of the crossover where RR switches from > 1.0 to < 1.0 or vice versa. RRs in the Table refer to the RR prior to the age of crossover. For example, RR_{before 30-44 years} > 1.0 for parity compared with nulliparity; whereas after age 44 years, RR < 1.0 for parity compared with nulliparity. Parity increases breast cancer risk before ages 30-44 years but is protective thereafter.^7,12 Obese BMI (body mass index) is protective for premenopausal women before age 50 years but increases risk for postmenopausal women.⁸ Age-specific incidence rates are higher for blacks than whites prior to age 40 years but higher for whites after age 40 years.⁹ Poor prognostic factor characteristics (tumor sizes > 2.0 centimeters, positive axillary lymph nodes, high tumor grade, estrogen and progesterone receptor negative expression) are more common among women before age 50 years, whereas good prognostic factors are more common after age 50 years.¹⁰ Breast cancer outcome (overall recurrence rate and greater risk for developing metastatic disease) is worse among younger (before age 35 years) than older patients, and this difference is not fully explained by greater frequency of adverse prognostic factors.³⁸ Adjuvant systemic therapy is associated with higher rates of relapse for ER+ breast cancers among women before age 35 years than older women.⁴ NSABP B18 showed that neoadjuvant (preoperative) chemotherapy was marginally beneficial among women before age 50 years and the reverse was true for older women.⁵ Fenretinide chemoprevention demonstrated borderline protective effects (P = .045) for premenopausal women before age 51 years and harmful effects for postmenopausal women.⁶

Abbreviations: RR, relative risk; BMI, body mass index; ER, estrogen receptor; PR, progesterone receptor; Rx, treatment; NSABP, National Surgical Adjuvant Breast and Bowel Project; AC, doxorubicin and cytoxan.