Everolimus shows a large interpatient variability with fixed dose administration. These very different exposure levels between individuals can result in supratherapeutic or subtherapeutic exposure levels and consequently in over- or undertreatment, respectively. Dose individualization based on the measured drug concentration could theoretically result in less toxicity and more efficacy.

Nowadays everolimus exposure is determined by everolimus concentration in whole blood. Therefore, a vena puncture is always necessary. This is invasive and requires patients to come to the hospital. It would be convenient for patients to have their everolimus blood concentration determined by dried blood spot (DBS) analysis. With DBS only a single drop of blood from the finger is necessary, which can be done at home and sent by regular mail for analysis. Previous studies have shown the feasibility of this approach. In patients with cancer treated with everolimus 10mg once daily, the correlation between everolimus DBS concentrations and whole blood concentration is yet unknown. Therefore, the investigators want to determine the everolimus concentration collected with DBS from a finger prick with everolimus concentration from whole blood and everolimus concentration collected with DBS from whole blood.

In addition, possibly a relatively high everolimus concentration in saliva could be correlated with the incidence and severity of oral mucositis. Determination of drug concentration in saliva has also been proven to be feasible before.

Therefore, in this study the investigators want to determine whether the everolimus concentration in saliva correlates with the incidence of oral mucositis and how everolimus concentration in saliva correlates with everolimus concentration in whole blood.

Inclusion Criteria:

• Patients currently treated with everolimus for any type of cancer
• Patients from whom it is possible to collect blood samples
• At least 18 years of age
• Able and willing to sign the Informed Consent Form prior to study assessments.

Exclusion Criteria:

• None

Patients who are currently treated with everolimus for any type of cancer are eligible in this study.