Comparing the effectiveness of stimulation using rhTSH and thyroid hormone withdrawal in the treatment of thyroid cancer

Thyroid cancer (TC) is the most common neoplasm of the endocrine system. In 2011, the standardized incidence rate in Poland was 7.4 for women and 1.7 for men [1]. This rate is characterized by a steady increase. However, it is not accompanied by an increase in mortality [2,3]. On the contrary, a significant reduction is observed due to diagnosing cancer at earlier stages and improved treatment effectiveness [4]. Over 90% of all TC are differentiated thyroid cancers (DTC), which are characterized by favorable prognosis, i.e. 10-year survival in 90-95% of cases [5]. As a result of treatment, more than 80% of patients recover, although in 15% of cases local recurrence is observed, with distant metastases being diagnosed in 5-10% of cases. Relapse frequently occurs within the first five years, but there have been reports of recurrences or distant metastases even 40 years later; therefore, lifetime oncological follow-up is required [6]. Taking into account the very good prognosis and the need for long-term monitoring, patients should be offered the safest and most comfortable procedures. The biggest burden for patients with DTC resulting from oncological treatment and follow up is the use of a radioiodine (I) and periods of hypothyroidism required to evaluate TSH-stimulated thyroglobulin (Tg) a sensitive and specific marker for DTC. The use of I is associated with a dose-dependent increase in the risk of secondary neoplasms: leukemia, bone cancer, stomach and colorectal cancer, salivary gland cancer and soft tissue tumors. Compared to the general population, in patients treated with I an overall 27% increase in the risk of other tumors was observed. The adverse effects of I are also manifested as impaired function of salivary glands, and parotid glands in particular [7,8]. Periods of hypothyroidism lasting for approximately 46 weeks are associated with disturbances in the patients’ symptoms of hypothyroidism, deteriorating patients’ physical, intellectual and social functioning. Additional treatment is often needed due to exacerbation of comorbid conditions and inability to work [9]. The introduction of recombinant human TSH (rhTSH) was a breakthrough in the care of patients with DTC. Recombinant human TSH (rhTSH) is a protein produced by the ovarian cell lines of Chinese hamsters transfected with DNA that encodes both subunits of the protein. The bioactivity of recombinant TSH depends on the degree of saturation of the carbohydrate component with the sialic acid residues, and is as high as for endoTSH in overt hypothyroidism and significantly higher than for endoTSH in the state of hormonal balance. Recombinant TSH strongly stimulates iodine uptake as well as Tg and thyroid hormone synthesis in both thyrocytes and DTC cells. The results of studies evaluating the impact of rhTSH on I pharmacokinetics are of great importance, indicating a decrease in isotope radiotoxicity (reduction of exposure dose for the bone marrow by a third) by accelerating the renal clearance of iodine and reduction of the effective half-life of I in the whole body from 0.54 +/0.1 day to 0.43 +/0.1 day. At the same time, the effective half-life of I is extended in the thyroid gland residues, which is a beneficial effect that determines effectiveness of the treatment [10-12]. Registered indications relate to the use of rhTSH for ablation in patients after total thyroidectomy with no evidence of distant metastases, as well as in monitoring the course of the disease. Numerous studies [13,14] confirm the equal effectiveness of ablation for I at 1100 MBq Endocrinology Department; Holycross Cancer Center, Kielce, Poland Kowalska Thyroid Research 2015, 8(Suppl 1):A16 http://www.thyroidresearchjournal.com/content/8/S1/A16