Metastatic renal cell carcinoma (mRCC) develops in approximately 33% of all renal cancer patients. First line treatment of mRCC includes drugs such as sunitinib, temsirolimus and pazopanib, with overall survival now reaching up to 43,6 months in patients with favorable-risk metastatic disease. Several side-effects in mRCC treatment, such as hypothyroidism, can be used as positive prognostic factors and indicate good response to therapy. Hypercholesterolemia and hypertriglyceridemia independent of hypothyroidism are reported as side-effects in temsirolimus treatment and recently in sunitinib treatment, but the exact mechanism and significance of the changes remains elusive. Most likely, metabolic changes are caused by inhibition of mechanistic target of rapamycin (mTOR), a positive target of tumor growth suppression, but also a regulator of iron homeostasis. There are no clinical studies reporting changes in iron and ferritin levels during mRCC biotherapy, but we hypothesize that inhibition of mTOR will also affect iron and ferritin levels. If both lipid and iron changes correlate, there is a high possibility that both changes are primarily caused by mTOR inhibition and the level of change should correlate with the inhibition of mTOR pathway and hence the efficacy of targeted treatment. We lastly hypothesize that mRCC biotherapy causes hypercholesterolemia with a possibly improved cholesterol profile due to increase HDL/LDL ratio, so statins might not have a role as supplementary treatment, whereas a sharp rise in triglyceride levels seems to be the primary target for additional therapy.