Abnormal thyroid function in breast cancer patients at initial diagnosis
Many non-thyroidal illness may affect the thyoid function and induce NTIS , which is also called euthyroid sick syndrome (ESS) , low T3 or T4 syndrome , marked by reductions in both thyroid function and peripheral conversion of T4 to T3, presumed to reflect a homeostatic mechanism to conserve energy. TSH levels tend to be normal or slightly decreased in these patients, but the underlying mechanism of reduced thyroid function is unknown. In this study, the NTIS prevalence in breast cancer patients at initial diagnosis was higher than that in breast benign lesions patients (16.5% vs 7.3%). The high NTIS prevalence in breast cancer patients at initial diagnosis suggests that NTIS may be related with malignancy. Furthermore, it was found in this study that the mean concentration of FT3 in breast cancer patients at initial diagnosis was significantly lower than that in breast benign lesions patients, suggesting that thyroid hypofunction may occur in breast cancer patients. Galton VA  studied the effect of malignant tumor on the thyroid function in rats, implanted with Walker 256 carcinosarcoma cell line, results showed a reduction in the concentration of T4 in tumorous rats serum, compared with corresponding control rats, due to the increased deiodination and urinary excretion.
The causes for hypothyroidism in cancer patient may not only be associated with tumor necrosis factor, interleukin-1, interferon-γ [17, 18], which inhibits the function of hypothalamus-pituitary-thyroid axis and peripheral conversion of T4 to T3, but also be associated with the self-protection mechanism, reducing the tissue metabolism to suppress the tumor growth.
Alteration of thyroid function of breast cancer patients during chemotherapy
Chemotherapy is one of the most effective systemic therapies for cancers. In cancer patients, thyroid function is thought to be vulnerable to chemotherapy, as hypothalamic-pituitary axis is active and chemotherapy is systemic therapy for patients. The influence of chemotherapy on thyroid function was just seen as a late effect, mainly presenting hypothyroidism. Only few studied the alterations of thyroid function during chemotherapy, which induced abnormalities in thyroid hormones metabolism with a significant decrease in serum T3 concentration (NTIS) instead of overt thyroid disease in malignant hematologic disease . Thyroid hypofunction was thought to be associated with inhibition of the liver thyroglobulin secretion  and hypothalamus-pituitary-thyroid axis function  by chemotherapy.
In this study, NTIS prevalence in breast cancer patients obviously increased during chemotherapy, compared with that at initial diagnosis (87.1% vs 16.5%) and then decreased to 15.4% before the next chemotherapy (prechemotherapy). The NTIS prevalence reduction from 16.5% to 15.4% indicated that chemotherapy alleviated the NTIS prevalence, as thyroid hypofunction is considered as risk for breast cancer occurrence  and poor prognosis , this also suggests that NTIS alleviation may be a good efficacy by chemotherapy. With significantly increased NTIS prevalence during chemotherapy, whether controlling it is better for enhancing chemotherapeutic efficacy is unclear.
Furthermore, during chemotherapy for breast cancer patients in this study, significant decreases of T3, T4, FT3 and TSH were found, compared with prechemotherapy (P<0.05). After chemotherapy, thyroid function began to recover, and there was no significant difference between two consecutive prechemotherapies (P>0.05), which indicated obvious thyroid function decreasing caused by chemotherapy mainly occurred during chemotherapy.
While there is still no detailed study on whether decrease of thyroid function goes against breast cancer chemotherapy or not. Decrease of thyroid function does not occur in all patients with malignant tumors during chemotherapy. In a prospective study, effects of chemotherapy on thyroid function in patients with non-seminoma testicular carcinoma were evaluted: Serum HCG was present in sixteen patients and absent in fifteen. HCG levels ranged from 10 to 30,000 μg/l, with a median value of 520 μg/l. And during chemotherapy, T4, T3 and rT3 levels increased significantly, but basal TSH levels and the TSH response to thyrotropin releasing hormone (TRH) decreased. Furthermore, after chemotherapy the increased T4 and lowered TSH levels returned to normal, while the FT3 level did not change either during or after chemotherapy , which suggested an unaltered hypothalamic / pituitary axis. Non-seminomatous germ-cell tumors (NSGCT) can comprise several different histological components, among which, choriocarcinoma, produces HCG. In NSGCT patients with high-serum HCG levels, hyperthyoidism has been recognized and is considered to be a paraneoplastic phenomenon. Hyperthyroidism frequently accompanies NSGCT with highly elevated HCG . Recent investigations have clarified the structural homology not only in the HCG and TSH molecules but also in their receptors, and this homology suggests the basis for the reactivity of HCG with the TSH receptor [24, 25]. Hyperthyroidism or increased thyroid function has been reported in many patients with trophoblastic tumors , either hydatidiform mole [27, 28] or choriocarcinoma , for which the principal therapy is chemotherapy. With effective chemotherapy, their long term survival exceeds 95% [24, 29]. Furthermore, hyperthyroidism can be cured after the healing of the trophoblastic tumors . Meister LH et al. reported a 26-year-old pregnant woman suffered from choriocarcinoma with metastases to both lungs. HCG were more than 2.5×106 mU/ml. Consistent with HCG-induced hyperthyroidism, the patient suffered from thyroid crisis with fever of 38.6°C, worsening respiratory distress, tachycardia of 140 bpm and mental confusion during the first cycle of chemotherapy. Then the patient was treated with antithyroid crisis, symptomatic and supportive treatments. After the 10th cycle of chemotherapy the patient was in good condition and free of metastatic lesions in her chest X-ray . It was reported that thyroid hormones could significantly promote the tumor growth and metastases . The effective chemotherapy of curable tumors (such as malignant hydatidiform mole, choriocarcinoma, etc.) may be associated with hyperthyroidism during chemotherapy, which may enhance the chemotherapeutic sensitivity by inducing tumor cells progression from G0-G1 phase into S phase or elevating the mitochondrial activity. While, in this study, thyroid function decreased significantly and majority of the breast cancer patients suffered NTIS during chemotherapy, which may be associated with decreased chemotherapy sensitivity. Therefore, based on the above analysis, it was hypothesized that increasing the thyroid function by giving thyroid hormones before and / or during chemotherapy to imitate the hyperthyroidism or high thyroid function state of some choriocarcinoma patients during chemotherapy may enhance the chemotherapeutic efficacy in breast cancer and other malignant tumor patients who suffer obviously decreased thyroid function or NTIS during chemotherapy.
Effect of triiodothyronine on chemosensitization
The effect of thyroid hormones on chemotherapeutic efficacy has been rarely researched before, and whether adding thyroid hormones during chemotherapy is suitable for breast cancer patients is still unknown. Some studies found hypothyroidism may be the protective factor for cancers, as hypothyroidism can suppress tumor growth , in addition, Hercbergs et al. found that hypothyroidism could reduce the insulin-like growth factor 1, the antagonist of tamoxifen-induced cytotoxicity, to prolong the survival in recurrent high grade glioma patients . This above mentioned perspective is different from our hypotheses, since we think hyperthyroid function is beneficial for treatment efficacy when patients receive chemotherapy. If patients of cancers reveive no chemotherapy, the status of hypothyroidism will be better for prognosis. Choriocarcinoma is curable with chemotherapy only, long term survival of these patients exceeds 95%, the underlying mechanism may refer with high levels of HCG, which can induce hyperthyroidism . In contrast, we firstly found thyroid hormones decreasing and NTIS prevalence increasing during chemotherapy in breast cancer patients, however, growth of breast cancer cells is regulated by thyroid hormones , thyroid hormones are considered to be the growth factor for glioma and thyroid cancer , the absence of thyroid hormones in cells could provoke a proliferation arrest in G0-G1  or weak mitochondrial activity , which makes tumor cells insensitive to chemotherapy.
Basing on these points, we performed T3 chemosensitization test in breast cancer cells. The normal FT3 concentration in human body is 2.2-4.2 ng/ml, we take the physiological concentration range of FT3 as the reference standard. Therefore, 4 ng/ml T3 was used firstly in cell culture medium which contains no thyroid hormones, to evaluate whether the physiological concentration of T3 can elevate the chemotherapeutic efficacy. 5-Fu, the chemotherapeutic regent mainly focusing on tumor cells in S phase, is a usual component in chemotherapy for breast cancer. The T3 pretreatment induced MCF-7 increased progression from G0-G1 phase to S phase, with elevated chemosensitivity to 5-Fu, the similar result was found in MDA-MB-231. Taxol works differently by arresting the breast cancer cells in G2-M phase, it enhances the polymerization of tubulin to stable microtubules and also interacts directly with microtubules, stabilizing them against depolymerization by cold and calcium, which readily depolymerize normal microtubules, so cells treated with taxol are unable to form a normal mitotic apparatus. To prove T3 can sensitize the breast cancer cells to Taxol, we used 24 ng/ml T3 to pretreat MCF-7 or MDA-MB-231, the results showed that both MCF-7 and MDA-MB-231 pretreated with T3 were more sensitive to Taxol than those with Taxol only, without T3 pretreatment.
Both MCF-7 and MDA-MB-231 express the thyroid hormone receptor, the chemosensitization role of T3 in these two cell lines is thought to be mediated by the proliferation efficacy of T3. In MCF-7, an estrogen receptor positive breast cancer cell line, the proliferative effect of thyroid hormone is not only initiated through the combination with the thyroid hormone receptor, but also through the combination with the estrogen receptor . There are specific mechanisms that explain why thyroid hormone stimulate cell proliferation in gastric cancer cells, the cyclin/cyclin-dependent kinase levels and activity are involved . Dinda et al.  found thyroid hormone not only enhances the phosphorylation of pRb, but also induces the c-Myc expression and mutant P53 expression, this can also explain the cell proliferation efficacy of thyroid hormone. MDA-MB-231 is acknowledged harboring P53 mutations, which further demonstrates that thyroid hormone may promote the cell proliferation. Furthermore, thyroid hormone was found to sensitize the mitochondrial pathway to enhance the chemotherapeutic efficacy in MDA-MB-231 .
Thyroid hormone exerts its non-genomic and genomic actions in breast cancer cells . For non-genomic action, which is characterized by combination of thyroid hormone and membrane receptors such as ER to elucidate the downstream signaling cascade, and is independent of transcriptional activity . For genomic action, thyroid hormone primary mode is by binding to the thyroid hormone receptor in the nucleus then influencing the transcription and expression patterns of target genes. In MCF-7, which expresses ER and thyroid receptor, the chemosensitization role of T3 is mediated through the genomic and non-genomic actions of T3, while in MDA-MB-231, which expresses thyroid receptor, the enhanced chemotherapeutic efficacy can also be contributed to the genomic and non-genomic actions of T3, like the influence on genes expression and the elevated mitochondrial activity mentioned above.
In light of the findings mentioned above, T3 may be used as adjuvant therapy for breast cancer patients in the future, the main points for its application are usage dose and how to combine it with chemotherapy. To imitate different usage modes of T3 in clinic, six individual groups with treatment by T3 and 5-Fu were set up to separately compare with control group treated with 5-Fu only. It is indicated in this results that, to get chemosensitization efficacy, pretreatment with lower dose of T3, using higher dose of T3 together with 5-Fu or during chemotherapy with 5-Fu were all thought to be available. In clinic, however, using higher dose of T3 will increase the risk of suffering thyroid crisis, and in most of T3 chemosensitization tests from 4 ng/ml to 32 ng/ml, the relative inhibition ratio in 1st group was highest, except T3 at 16 ng/ml and 24 ng/ml. So, pretreatment with lower dose of T3 until the end of chemotherapy may be a safer and more efficient therapy for breast cancer patients. In addition, only a suitable dose of T3 could have chemosensitization role in chemotherapy, treatment with extremely low dose of T3 for long time (72 h) still could not enhance the chemosensitivity of MCF-7 to 5-Fu.
Using T3 for chemosensitization in breast cancer therapy is to simulate the high thyroid function in choriocarcinoma patients during chemotherapy, based on the new findings that thyroid hormones decreasing during chemotherapy, in which chemotherapeutic regents mainly take effect.
In summary, we studied the thyroid hormones and NTIS in breast patients at initial diagnosis and during chemotherapy, in which with a thyroid function significant decreasing, and found T3 enhanced the chemosensitivity of MCF-7 to 5-Fu. Moreover, we think the chemotherapeutic efficacy partly depends on the thyroid function, checking the thyroid function in breast cancer patients is important for elevating chemotherapeutic efficacy.