Among 5101 women with stage I, stage II, or stage IIIA breast cancer diagnosed from 1991 through 1997 in New Mexico, age at diagnosis ranged from 20 to 98 years; the mean age was 61 years. presents the percentage of women receiving chemotherapy by tumor stage and patient age. Overall, 29% of women received chemotherapy, and the rate of chemotherapy use for stage I, stage II, and stage IIIA was 11%, 47%, and 68%, respectively. Across all tumor stages, the use of chemotherapy decreased substantially with increasing age (P < 0.001 for trend). Overall, 66% of women younger than 45 years of age received chemotherapy compared with 44% of women between 50 and 54 years of age, 31% of women between 55 and 59 years of age, and 18% of women between 60 and 64 years of age. Only 12% of women between 65 and 69 years of age and 3% of those older than 75 years of age received chemotherapy.
presents the use of chemotherapy by patient age, lymph node status, and hormone receptor status in women with stage I, stage II, or stage IIIA breast cancer. As expected, chemotherapy was used more often in women with node-positive tumors and women with estrogen receptor–negative tumors. However, across all classes of tumor characteristics, use of chemotherapy decreased substantially with age (P < 0.001 for trend). For example, in women with node-positive and hormone receptor–positive tumors, the percentage of women who received chemotherapy decreased as follows: 87% for women younger than 45 years of age, 67% for women 55 to 59 years of age, and 22% for women 65 to 69 years of age. Chemotherapy use was relatively stable in women with node-positive and hormone receptor–negative tumors who were younger than 65 years of age; however, use decreased substantially after age 65 years. In additional analyses that were stratified by node status (positive versus negative) and by tumor size, chemotherapy use decreased with age (data not shown).
presents chemotherapy use in relation to use of adjuvant hormone therapy (usually tamoxifen). The percentage of women who received chemotherapy plus hormone therapy or who received chemotherapy alone decreased with advancing age. The percentage of women receiving hormone therapy alone increased with age. However, the overall percentage of women with breast cancer who did not receive adjuvant therapy (neither chemotherapy nor hormone therapy) increased substantially with age.
Use of Adjuvant Chemotherapy and Adjuvant Hormone Therapy in Women with Stage I, Stage II, or Stage IIIA Breast Cancer from 1991 through 1997 in New Mexico by Patient Age
The presents the use of chemotherapy in women with breast cancer as a function of two variables: age and whether use of chemotherapy was clearly recommended in the 1990 NIH Consensus Conference (based on tumor characteristics). We examined women younger than 70 years of age with 1) node-positive tumors, 2) node-negative, hormone receptor–negative tumors larger than 1.0 cm in size, or 3) node-negative tumors of any hormone receptor status that were greater than 3.0 cm in size. Any other tumors were categorized as having no clear consensus recommendation, based on the 1990 Consensus Conference. As hypothesized, the use of chemotherapy in women with tumors for which no clear chemotherapy guidelines existed decreased sharply with age, falling to less than 10% for women 55 years of age and older. However, we observed an almost parallel decrease in the use of chemotherapy with age in women with tumors for which chemotherapy was generally recommended. In these women, 77.4% of those who were younger than 45 years of age received chemotherapy. In contrast, chemotherapy was given to only 58.1% of those 55 to 59 years of age, only 37.7% of those 60 to 64 years of age, and only 25.0% of those 65 to 69 years of age.
Receipt of adjuvant chemotherapy as a function of age and tumor characteristics in women with breast cancer
presents a multivariable analysis of the effect of age on the adjusted odds of receiving chemotherapy in women with breast cancer. We then converted the parameters used to generate odds ratios and their confidence intervals to probabilities (22
). We obtained the probability of receiving chemotherapy for each age group, holding constant race, tumor stage, node status and hormone receptor status, surgery and radiation therapy status, and adjuvant hormone therapy use across age groups. We observed the same pattern seen in the bivariate analyses of declining chemotherapy use with age (, , and and ). Younger women with breast cancer had a greater chance of receiving adjuvant chemotherapy, and, as expected, women older than 70 years of age were least likely to be given chemotherapy.
Multivariable Analysis for the Odds or Probability of Receiving Chemotherapy in Women with Stage I, Stage II, or Stage IIIA Breast Cancer from 1991 through 1997 in New Mexico
We also conducted sensitivity analyses to estimate the potential effect of unknown confounders on the study results. These analyses demonstrated that the relationship between age and chemotherapy use in our large population-based setting was relatively insensitive to confounding by unmeasured factors. For example, let us examine the following scenario: The prevalence of an unmeasured confounding variable is 90% in women younger than 50 years of age and 50% in women 50 years of age or older. The odds ratio for receipt of chemotherapy associated with this unmeasured confounder is 2.0. Thus, the adjusted odds ratio of receiving chemotherapy for the women in the 55- to 59-year-old age group relative to women younger than 45 years of age would be 0.25 (95% CI, 0.19 to 0.34) instead of 0.21 (CI, 0.16 to 0.29), as shown in . However, under extreme conditions, the effect of age on chemotherapy use could be affected. If the prevalence of an unmeasured confounding variable were 90% in women younger than 50 years of age and 10% in women 50 years of age and older and if the odds ratio for receiving chemotherapy associated with this unmeasured confounder were 5.0, the adjusted odds ratio of receiving chemotherapy for the 50- to 54-year-old age group relative to the group younger than 45 years of age would become insignificant (0.79 [CI, 0.58 to 1.07]). Even under such extreme circumstances, the age groups 55 to 59 years of age and 60 to 64 years of age relative to the group younger than 45 years of age are still significantly associated with decreasing use of chemotherapy. However, the significance is reduced to 0.43 (CI, 0.31 to 0.59) for women 55 to 59 years of age and reduced to 0.19 (CI, 0.14 to 0.27) for women 60 to 64 years of age compared with women younger than 45 years of age. In addition, we used two different approaches for a small number of women with missing information on chemotherapy and hormone therapy use: We excluded these women from the total number of women or recorded them as not having received therapy. The results showed little difference in the relationship between age and chemotherapy use, although overall rate of chemotherapy use was slightly altered (data not shown).