Smell and taste function after completion of childhood cancer treatment: Follow-up of a prospective cohort study

Background & aims: Smell and taste changes are common and bothersome treatment symptoms during childhood cancer treatment, consequently affecting food intake and quality of life. Patients frequently ask whether and when smell and taste function recover after childhood cancer treatment. However, this question is difficult to answer as available evidence is sparse and limited to cross-sectional designs. The current study aims to describe the prevalence of (both objective and subjective) smell and taste dysfunction, and its relation with dietary intake and Health-related Quality of Life (HRQoL) within five years post-treatment. Methods: In this follow-up of a previous prospective cohort study, 66 Children, Adolescents and Young People (CAYA) treated for hematological, solid, or brain malignancies were included. Data on smell (odor threshold and identification; Sniffin’ Sticks), taste (Taste Strips), dietary intake (3-day food diary), and HRQoL (total, physical, psychosocial; PedsQL 4.0 Generic Core Scales) were collected within five years post-treatment and compared with previous data collected during maintenance phase (acute lymphoblastic leukemia, ALL)/within three months after completion of treatment (other diagnosis). Correlations between smell and taste, and dietary intake and HRQoL were assessed one to five years post-treatment. Results: Odor identification scores were significantly higher within five years post-treatment (median 11.0, IQR 10.0–12.0) compared to three months after completion of treatment (median 10.0, IQR 9.0–11.0), but not for CAYA with ALL during maintenance treatment. According to odor threshold cut-off values, CAYA with ALL were more often considered hyposmic within five years post-treatment, whereas hyperosmia increased in CAYA with other diagnosis. Only 47.8% of CAYA with ALL and 67.4% of CAYA with other diagnoses showed normal taste perception, showing a shift toward both hypo- and hypergeusia. Self-reported smell and taste changes declined within five years post-treatment, with smell changes ranging from 8.7% to 14.0% and taste changes from 27.9% to 43.5%. Results show a moderate positive correlation between objective taste function and both total HRQoL (r = 0.306, 95% CI 0.041–0.530) and psychosocial HRQoL (r = 0.336, 95% CI 0.075–0.554), and a moderate negative correlation between odor identification and dietary intake (r = −0.343, 95% CI -0.603 to −0.016). Conclusion: Even years after completing childhood cancer treatment, many CAYA continue to objectively exhibit reduced or heightened smell and taste sensitivity. While self-reported smell and taste changes decline over time, more than one third of CAYA still experience taste changes within five years post-treatment. This appears to be most pronounced among CAYA treated for ALL. It should be noted that subjective reports are not always confirmed by psychophysical testing, particularly for enhanced smell, suggesting that olfactory intolerance may be a more appropriate term than hyperosmia. In addition, the small, heterogeneous sample limits generalizability. Nevertheless, early identification of sensory changes is important to minimize adverse health consequences.