Evening salivary cortisol as a single stress marker in women with metastatic breast cancer.

Background: Flattened diurnal salivary cortisol patterns predict shorter subsequent survival with breast, lung, and renal cell carcinomas. The underlying cause of this flattened slope is undetermined, though it has been hypothesized to be secondary to a deficit in the amplitude of the circadian clock. To gain greater insight into the portions of the diurnal salivary curve that are associated with cancer survival, we examined (1) which points in the diurnal curve are predictive of the slope of the curve and (2) whether elevated evening cortisol levels alone are associated with reduced HPA-axis feedback inhibition (i.e., decreased sensitivity to the dexamethasone suppression test).

Method: We examined study hypotheses on adult women with advanced breast cancer (age = 54.3 ± 9.58 years; n = 99) using non-parametric Wilcoxon's rank-sum tests, Spearman correlation coefficients and an accuracy formula based on a confusion matrix. Cortisol was sampled five times per day for three consecutive days, with dexamethasone administered late on the second day.

Results: Salivary cortisol concentrations did not vary between those with flat and steep slopes during the morning (p's > .05), but did vary in the evening (p's < 0.05). Furthermore, the concentration of the 2100h alone was 86% accurate in discriminating between individuals classified as having "flat" or "steep" slopes. Dexamethasone suppression was only associated with diurnal salivary cortisol slope (p = .0042).

Conclusions: Evening cortisol levels are a sensitive indicator flattened diurnal cortisol slope, suggesting evening cortisol may also be a useful predictor of breast cancer survival. Future research should focus on determining the causes of abnormally increased evening cortisol.