Post-surgical treatment of thyroid carcinoma in dogs with retinoic acid 9 cis improves patient outcome

Abstract

The objective of the present study was to compare the effects of isotretinoin 9-cis (RA9-cis) as a post-surgery treatmentof thyroid carcinoma to a traditional treatment (doxorubicin) and no treatment. Owners who did not want their dogsto receive treatment were placed into the control group A (GA; n=10). The remaining dogs were randomly placed intoeither group B (GB; n=12) and received doxorubicin at a dose of 30 mg/m2 every three weeks, for six complete cyclesor group C (GC; n=15) and treated with RA9-cis at a dose of 2 mg/kg/day for 6 months. The time of the recurrencewas significantly shorter in the GA and GB compared to GC (P=0.0007; P=0.0015 respectively), while we did notdetect differences between GA and GB. The hazard ratio of recurrence between GA and GB compared to GC were7.25 and 5.60 times shorter, respectively. We did not detect any differences between the other groups. The risk ratioof recurrence was 2.0 times higher in GA compared to GC and 2.1 times higher in GB compared to GC. The typeof carcinoma had an effect on time of survival with follicular carcinomas having an increased mean survival timethan follicular-compact carcinomas (P<0.0001) and follicular-compact carcinomas had a longer mean survival timethan compact carcinomas. The interaction among treatment and type was significant, but survival time in follicularcarcinomas did not differ between treatments. In follicular-compact carcinomas the survival time of GC was greaterthan GB (P<0.05), but we did not detect a difference between GA and GB. In conclusion, this study shows that theuse of surgery in combination with RA9-cis treatment significantly increases survival rate and decreases the timeto tumor recurrence when compared to doxorubicin treated or untreated dogs. The histological type of carcinomainteracted with treatment for time to recurrence and survival time, with more undifferentiated carcinomas having aworse prognosis than differentiated carcinomas.