Correspondence of plasma and salivary cortisol patterns in women with breast cancer.

INTRODUCTION: The 'diurnal slope' of salivary cortisol has been used as a measure of stress and circadian function in a variety of reports with several detailing its association with cancer progression. The relationship of this slope, typically a negative value from high morning concentrations to low evening concentrations, to the underlying daily variation in total plasma cortisol throughout the 24-hour cycle, however, has never been reported.
METHODS: To examine the relationship between the diurnal salivary cortisol slope and the underlying pattern of plasma cortisol in individuals with cancer, we examined a cohort of women with advanced breast cancer (n = 97) who had saliva and plasma collected during a modified 24-hour, constant posture protocol.
RESULTS: We found that the steepness of the diurnal slope of salivary cortisol was correlated with the amplitude of plasma cortisol rhythm when the slope was calculated from samples taken at wake + 30 min and 9 PM (r = -0.29, p > 0.05). Other variants of salivary slope calculations were not significantly correlated with the amplitude of the plasma cortisol rhythm. Diurnal salivary cortisol slope steepness was not correlated with the time between habitual waking and the computed circadian peak of cortisol, but there was a correlation between diurnal slope steepness and the time between habitual waking and the time of the awakening spike of morning cortisol (r values <-0.23, p values <0.05).
CONCLUSION: It therefore appears that in women with advanced breast cancer, diurnal salivary cortisol slope primarily represents aspects of the cortisol awakening response in relation to evening levels more than the circadian rhythm of total plasma cortisol.