LT3 treatment still considered ‘experimental’
Despite the dramatic increase in LT3 prescribing in recent years noted by the authors, as many as five systematic reviews/meta-analyses have shown no superiority of combination therapy over LT4 alone in terms of hypothyroid symptoms, quality of life, or patient preference.
As a result, many international guidelines still consider the combination-treatment approach to be experimental.
Other trials that have raised concerns about the combination include previous large, prospective Swedish studies that have linked higher endogenous T3 levels to breast cancer in postmenopausal women.
As for the mechanism, some small experimental studies have suggested an estrogenlike effect whereby T3 could enhance the proliferation of breast cancer cells.
On a broader level, thyroid hormones, in general, have been extensively studied in cancer research as possibly promoting cancer cell proliferation in a variety of cancer types.
However, the current findings should lay some of those concerns to rest, Dr. Planck reiterated: “Our data provide reassuring evidence regarding the risk of cancer and mortality.”
“We did not identify any increase in breast cancer incidence, any cancer incidence, all-cause mortality, any cancer mortality, or breast cancer mortality between individuals using LT3 and LT4 treatment.”
The authors and Nguyen have reported no relevant financial relationships.
A version of this article first appeared on Medscape.com.