Our analyses regarding predictors of chemotherapy-related nausea from the combined sample of 1696 patients following their first treatment yielded six findings of interest: 1) strong evidence that breast cancer patients experience significantly greater nausea than other patients, 2) confirmation of prior reports that younger patients experience greater nausea than older patients, 3) a new finding that perceived susceptibility to nausea is a significant predictor of actual nausea, 4) evidence that expectancy is a predictor of nausea, 5) the incidence of any severe nausea and any vomiting have a strong relationship, and 6) contrary to many prior reports, gender is not a significant predictor of nausea. Each of these findings is discussed below.
In the present analyses, we compared average nausea and incidence of severe nausea in breast cancer patients receiving doxorubicin to three other groups of patients. One of these groups was comprised of other patients receiving doxorubicin, typically those with hematologic cancers, and they would likely have received a lower dose of doxorubicin than the breast cancer patients. A second group was comprised of patients receiving cisplatin. The third group of patients received carboplatin. Our analyses showed that breast cancer patients receiving doxorubicin had significantly greater average nausea and a higher incidence of severe nausea than patients in the other three groups. Thirty-two percent of the breast cancer patients experienced severe nausea compared to less than 20% of patients receiving cisplatin and less than 10% of patients receiving carboplatin. Virtually all of the breast cancer patients in our study received not only doxorubicin but also cyclophosphamide, and it is possible that it is this particular combination of drugs that caused the high level of nausea observed in these patients rather than the doxorubicin alone.
Our finding that age is a significant predictor of nausea is not surprising; it has been reported many times previously.[3
] In the present analyses, because of our large sample size, we were able to divide age into five categories (<40, 40–49, 50–59, 60–69, ≥ 70) rather than the dichotomous category of younger or older than 50 years that is often reported in the literature.[6
] Mean nausea decreased with age category, with patients in the oldest category having average nausea that was one point less on the 7-point scale than patients in the youngest age category. Incidence of severe nausea ranged from over 50% of patients in the youngest cohort to less than half that in each of the two oldest cohorts. These analyses were done only in female breast cancer patients receiving doxorubicin-based treatments as a method of controlling for cancer and type of treatment; therefore, we are not sure if this will generalize to men and other cancer treatments.
The simple question of whether patients believed that they were more susceptible to nausea than their friends or family was a substantial determinant of average nausea in our sample. We examined the predictive role of susceptibility only in female breast cancer patients receiving doxorubicin-based treatments, our largest homogenous patient group. Taking into account age, expectancy and education, patients rating themselves more susceptible to nausea had significantly greater average nausea than patients rating themselves less susceptible. They were also nearly three times as likely to experience severe nausea. Patients who rated their nausea susceptibility about the same as friends and family members fell close to midpoint between the other two patient groups in both average nausea and incidence of severe nausea.
In a similar vein, and in the same patient sample, nausea expectancy was a significant predictor of average nausea, even after controlling for age and perceived susceptibility. Individuals expecting nausea, whether because they consider themselves to be very susceptible to nausea or for any other reason, may be more likely to interpret vague or ambiguous sensations as nauseating than an individual not expecting the symptom.[28
] The idea that perceptions are influenced by expectations in this way is a well established principle in the study of cognition.[29
We report on one analysis regarding vomiting, that is, the relationship between severe nausea and vomiting. Far more patients reported vomiting (827) than severe nausea (490) and fewer than half (48%) of those reporting at least one incidence of emesis also reported having severe nausea. On the other hand, of the 490 patients reporting severe nausea, 80% reported at least one episode of emesis. These findings suggest that the occurrence of vomiting is a strong contributing factor to the report of severe nausea but that the two symptoms are clearly different because over half of the patients reporting emesis do not report having severe nausea.
We did not find a significant relationship between gender and nausea. We conducted these analyses on 299 (male = 155) patients with gender neutral cancers, i.e., excluding patients with breast, genitourinary, or gynecological cancers. Regression analysis controlling for age, education, chemotherapy type, and study arm showed that gender did not significantly predict average nausea or incidence of severe nausea in these 299 patients. Our findings are contrary to much of the current literature regarding the relationship between gender and nausea in cancer patients, and we speculate that this contradiction is due to our using a sample of patients with only gender neutral cancers in our analyses. Considering our previously discussed finding that breast cancer patients receiving doxorubicin have significantly more nausea than other patients, we speculate that prior reports showing an effect of gender on nausea that included breast cancer patients in their analyses are in error because they did not adequately control for the significantly higher level of nausea in breast cancer patients receiving doxorubicin. Further research on the effect of gender on nausea will be needed to determine if this hypothesis is correct.