Extent and Incidence of Pseudo‐Worsening of Kidney Function Due to Oral Antitumor Therapeutics in the <scp>AMBORA</scp> Cohort: An Analysis of Real‐World Data

A considerable number of oral antitumor therapeutics (OAT) has the potential for causing pseudo-worsening of kidney function (PW) due to inhibition of renal creatinine secretion, i.e., kidney function is unaffected, while creatinine-based calculation of glomerular filtration rate (eGFR) erroneously indicates an impaired kidney function. Nonrecognition of PW can lead to dose reductions, interruptions, or discontinuations of OAT. The extent and incidence of PW has so far not been studied for a broad set of OAT in clinical routine. In this retrospective, multicenter cohort study, 694 AMBORA patients newly started on OAT were assessed for eligibility. eGFR values were compared between baseline and within 30 days of treatment. OAT were separated into the groups unlikely causing and likely causing/with proven PW. The usage of cystatin C measurements as an alternative method for assessing kidney function was evaluated. A total of 238 patients received 38 OAT likely causing PW/with proven PW. In this group, eGFR decreased significantly (-6.8 ml/min, p < 0.001). In 17.2% of these patients, eGFR decreased by ≥20 ml/min. Significant decreases in eGFR were observed for patients receiving, for example, abemaciclib, ribociclib, and osimertinib. Cystatin C measurements were not performed in 95.8% of the patients. In the group of 67 patients receiving OAT unlikely causing PW, there was no significant change in eGFR. In clinical routine, multiple OAT associated with PW are prescribed. A very low rate of usage of creatinine-independent methods for assessing kidney function (cystatin C) indicates that further training of oncologists is required on OAT-induced PW to further improve patient safety.