Human kallikrein 2 (hK2) mRNA in peripheral blood of patients with thyroid cancer: a novel molecular marker?

Circulating thyroid cancer markers

PURPOSE OF REVIEW

To describe the progress in the field of circulating markers of thyroid cancer.

RECENT FINDINGS

Thyroid cancer cells in the circulation can be detected by measuring the mRNA of thyroid-specific genes. Among these, thyroglobulin, and more recently thyroid-stimulating hormone receptor mRNAs' provide high diagnostic sensitivity and specificity for thyroid cancer detection. These markers can be used in synergy with current diagnostic modalities, i.e. fine-needle aspiration and ultrasound, for preoperative diagnosis and serum thyroglobulin measurement for monitoring.

SUMMARY

For the detection of recurrent/residual thyroid cancer, serum thyroglobulin remains the sole circulating marker, but lacks sensitivity and is unreliable in the presence of antithyroglobulin antibodies. The measurement of thyroid-specific mRNA in blood may provide sensitive/specific markers, but significant variability exists among various studies for thyroglobulin mRNA in particular, questioning the validity of this marker. Recent studies have demonstrated the high sensitivity and specificity of thyroid-stimulating hormone receptor mRNA in detecting recurrent/residual disease even in the presence of thyroglobulin antibodies. Fine-needle aspiration biopsy is currently the sole method for evaluating thyroid nodules. Indeterminate fine-needle aspiration cytology is found in approximately 15-30% of specimens. Thyroid-stimulating hormone receptor mRNA measurement in patients with indeterminate fine-needle aspiration may enhance cancer detection and save unnecessary surgeries.

Workshop on Cancer Biometrics: Identifying Biomarkers and Surrogates of Cancer in Patients

The current excitement about molecular targeted therapies has driven much of the recent dialog in cancer diagnosis and treatment. Particularly in the biologic therapy of cancer, identifiable antigenic T-cell targets restricted by MHC molecules and the related novel stress molecules such as MICA/B and Letal allow a degree of precision previously unknown in cancer therapy. We have previously held workshops on immunologic monitoring and angiogenesis monitoring. This workshop was designed to discuss the state of the art in identification of biomarkers and surrogates of tumor in patients with cancer, with particular emphasis on assays within the blood and tumor. We distinguish this from immunologic monitoring in the sense that it is primarily a measure of the tumor burden as opposed to the immune response to it. Recommendations for intensive investigation and targeted funding to enable such strategies were developed in seven areas: genomic analysis; detection of molecular markers in peripheral blood and lymph node by tumor capture and RT-PCR; serum, plasma, and tumor proteomics; immune polymorphisms; high content screening using flow and imaging cytometry; immunohistochemistry and tissue microarrays; and assessment of immune infiltrate and necrosis in tumors. Concrete recommendations for current application and enabling further development in cancer biometrics are summarized. This will allow a more informed, rapid, and accurate assessment of novel cancer therapies.

Expression of prostate-specific antigen (PSA) and human glandular kallikrein 2 (hK2) in ileum and other extraprostatic tissues

Prostate-specific antigen (PSA) is a widely used marker for prostate cancer. In the literature, there are reports of nonprostatic expression of PSA that potentially can affect early diagnosis. However, the results are scattered and inconclusive, which motivated us to conduct a more comprehensive study of the tissue distribution of PSA and the closely related protein human glandular kallikrein 2 (hK2). RT-PCR, in situ hybridization and immunohistochemistry were used to detect expression of both PSA and hK2 in secretory epithelial cells of trachea, thyroid gland, mammary gland, salivary gland, jejunum, ileum, epididymis, seminal vesicle and urethra, as well as in Leydig cells, pancreatic exocrine glands and epidermis. Immunometric measurements revealed that the concentration of PSA in nonprostatic tissues represents less than 1% of the amount in normal prostate. Pronounced expression of PSA was detected in the Paneth cells in ileum, which prompted us to compare functional parameters of PSA in ileum and prostate. We found that in homogenates from these 2 tissues, PSA manifested equivalent amidolytic activity and capacity to form complexes with protease inhibitors in blood in vitro. Thus, PSA released from sources other than the prostate may add to the plasma pool of this protein, but given the lower levels detected from those sites, it is unlikely that nonprostatic PSA normally can interfere with the diagnosis of prostate cancer. Nevertheless, this risk should not be neglected as it may be of clinical significance under certain circumstances. Supplementary material for this article can be found on the International Journal of Cancer website at http://www.interscience.wiley.com/jpages/0020-7136/suppmat/index.html.

Evaluation of circulating thyroid-specific transcripts as markers of thyroid cancer relapse

Circulating thyroid-specific transcripts have been suggested as potential molecular markers of residual or recurrent thyroid cancer. We assessed the accuracy of real-time RT-PCR-based detection of a panel of thyroid-specific markers, including TG, TPO, TSHR, NIS and PDS, in comparison with serum TG measurements in a series of 55 patients operated for differentiated thyroid cancer (DTC). Serum TG levels were higher in patients with residual thyroid tissue or metastatic cancer than in disease-free patients during thyroid hormone suppressive therapy (THST) and after stimulation with rhTSH (P < 0.05). Recombinant hTSH increased serum TG values in patients with tumor relapse (P < 0.05), but not in disease-free patients. This assay showed high specificity and good sensitivity in detecting tumor relapse (accuracy under THST = 81.4%; after rhTSH stimulation = 90.9%). TPO and TSHR mRNA, either under THST or after rhTSH, showed a significant correlation with disease status for molecular assays. Qualitative analysis of baseline and stimulated TG, NIS and PDS mRNA showed high sensitivity but low specificity in the prediction of thyroid cancer recurrence or metastases (accuracy under THST = 51%, 43% and 54%, respectively), whereas TPO and TSHR mRNA assays had higher specificity but low sensitivity, with accuracy under THST of 67% and 61%, respectively, that improved when these tests were combined. Our findings indicate that serum TG assay after TSH stimulation is the most accurate test for monitoring DTC. Combined measurements of TPO and TSHR mRNA levels during THST may represent a specific test for early detection of DTC relapse.