Low T3 syndrome as a predictor of poor prognosis in chronic lymphocytic leukemia

Low triiodothyronine (T3) state is associated with poor prognosis in critical acute and prolonged illness. However, the information on thyroid dysfunction and cancer is limited. The aim of our study was to evaluate the prognostic value of low T3 syndrome in chronic lymphocytic leukemia (CLL). Two hundred and fifty-eight patients with detailed thyroid hormone profile at CLL diagnosis were enrolled. Low T3 syndrome was defined by low free T3 (FT3) level accompanied by normal-to-low free tetraiodothyronine (FT4) and thyroid-stimulating hormone (TSH) levels. A propensity score-matched method was performed to balance the baseline characteristics. Multivariate Cox regression analyses screened the independent prognostic factors related to time-to-first-treatment (TTFT) and cancer-specific survival (CSS). Area under the curve (AUC) assessed the predictive accuracy of CLL-International Prognostic Index (IPI) together with low T3 syndrome. The results showed that 37 (14.34%) patients had low T3 syndrome, which was significantly associated with unfavorable TTFT and CSS in the propensity-matched cohort, and it was an independent prognostic indicator for both TTFT and CSS. Serum FT3 level was positively related to protein metabolism and anemia, and inversely related to inflammatory state. Patients with only low FT3 demonstrated better survival than those with synchronously low FT3 and FT4, while those with synchronously low FT3, FT4 and TSH had the worst clinical outcome. Low T3 syndrome together with CLL-IPI had larger AUCs compared with CLL-IPI alone in TTFT and CSS prediction. In conclusion, low T3 syndrome may be a good candidate for predicting prognosis in future clinical practice of CLL.