Role of Tg levels as a biomarker in RAI-R DTC during MKI is unclear. Falling levels of Tg after starting MKI treatment has been previously reported, with a higher reduction in patients who achieve response. However, transient Tg oscillations are a common phenomenon during therapy without a clear correlation with progressive disease (PD). In the present study, we analyze the correlation between Tg oscillations and progression-free survival (PFS) in patients with RAI-R DTC during MKI treatment.
Thirty-seven consecutive patients were reviewed. Inclusion criteria were: pathology confirmed RAI-R DTC, age >18 years, MKI treatment in the first or second line and serial Tg determinations along with the follow-up. Variations in Tg levels during MKI treatment were evaluated. As exploratory hypothesis, we considered the “Tg elevation non-PD related”, defined as a significant elevation of Tg higher than 50% compared with previous measure, not related with PD by RECIST criteria, followed by a Tg reduction in a subsequent determination, in patients with an initial Tg reduction after starting MKI treatment.
33 patients were included in the final analysis. Most MKI treatments were Sorafenib (44%), Lenvatinib (27%), Vandetanib (10%) and Axitinib (8%). Median duration of treatment was 15.5 months, and median PFS 20.2 months. Patients with any Tg levels reduction compared with baseline along MKI treatment showed a better PFS (23.5 vs. 3.6 months, p < 0.001). A Tg reduction >50% from baseline on the first month after starting MKI also had a benefit in PFS (27.7 vs. 14.2, p 0.02). 20.6% of cases had the nadir of Tg response beyond the first month of treatment. 34.4% of cases presented Tg elevation non-PD related along with follow-up (median number of elevations per patient: 2), with a better PFS compared with patients with other Tg oscillation patterns (29.9 vs. 15.5 months, p0.008).
Tg elevation non-PD related was associated with a better PFS compared with patients with other Tg variation patterns. Treatment with MKIs should not be stopped or changed based on Tg variations.
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J. Hernando Cubero: Speaker Bureau / Expert testimony: Eisai, Ipsen, Roche, Angelini Pharma; Travel / Accommodation / Expenses: Ipsen, Novartis, AAA, Roche, AstraZeneca, Eisai. All other authors have declared no conflicts of interest.