{"id":5923,"date":"2020-08-26T09:48:03","date_gmt":"2020-08-26T09:48:03","guid":{"rendered":"https:\/\/clinlabint.3wstaging.nl\/tshr-mrna-a-peripheral-blood-marker-to-diagnose-differentiated-thyroid-cancer\/"},"modified":"2021-01-08T11:39:40","modified_gmt":"2021-01-08T11:39:40","slug":"tshr-mrna-a-peripheral-blood-marker-to-diagnose-differentiated-thyroid-cancer","status":"publish","type":"post","link":"https:\/\/clinlabint.com\/tshr-mrna-a-peripheral-blood-marker-to-diagnose-differentiated-thyroid-cancer\/","title":{"rendered":"TSHR mRNA: a peripheral blood marker to diagnose differentiated thyroid cancer"},"content":{"rendered":"

Thyroid cancer is the most common endocrine malignancy and the fastest-growing cancer in terms of incidence rates to affect women. In the last decade, thyroid cancer rates have increased in most populations worldwide. Enhanced diagnostic tools for thyroid cancer have become available and stand to impact decision-making in patient care, the extent of surgical treatment, and prognosis in long-term follow-up. This article discusses how the novel blood test TSHR mRNA plays a role in these clinical scenarios.<\/strong><\/p>\n

by Dr Mira Milas and Dr Manjula Gupta <\/strong><\/p>\n

Differentiated thyroid cancer is represented most frequently by papillary thyroid cancer and follicular thyroid cancer, with other histological variants in the mix. These cancers originate from the follicular cells which comprise the thyroid gland and produce the protein thyroglobulin (Tg) and also the essential hormones thyroxine (T4) and triiodothyronine (T3). Unlike medullary thyroid cancer, where calcitonin elevation measured from a simple blood test is virtually diagnostic of the disease, papillary and follicular cancers have no such marker. Tg functions only to detect thyroid cancer recurrence in the absence of the thyroid gland, not pre-operatively. Thus, the mainstay of initial diagnosis of the differentiated thyroid cancers has been cytology, obtained by fine needle aspiration biopsy (FNAB) of thyroid nodules that are detected by exam or by ultrasound imaging [1].<\/p>\n

FNAB would be an excellent diagnostic tool if it allowed reliable and consistent diagnosis of differentiated thyroid cancers, but it has several limitations. Its sensitivity and specificity overall are 95% and 48%, and the positive and negative predictive values are 68% and 89%, respectively [2]. When the aspirate from a thyroid nodule contains all the morphologic features of papillary thyroid cancer, FNAB is 99% accurate in designating this malignancy. However, up to 40% of aspirates are abnormal but cannot be classified into a malignant subtype. Follicular thyroid cancer and the follicular variant of papillary thyroid cancer are examples of this \u2013 there are simply no morphological changes specific enough to allow recognition of such cancers via microscopic examination of biopsy samples. Additional complexity comes from the considerable variability among interpretations of thyroid cytology samples, both among different pathologists and when the same pathologist views the same sample at different times [2]. In 2008, a new classification system – the Bethesda system for reporting thyroid cytopathology – was developed to address this variability [3].<\/p>\n

For those patients with thyroid nodules whose FNAB results fall into an abnormal category without definitive evidence of malignancy (Bethesda categories III, IV, V), the traditional management algorithm has relied on surgery to enable diagnosis. Although thyroidectomy in expert hands has low complication rates, these are still measurable, and most notable for the 1-3% risk of permanent voice hoarseness. Most thyroid specialists have long appreciated that using thyroid surgery in this diagnostic capacity is not ideal, especially when 60-80% of patients will be found to have benign thyroid histology.<\/p>\n

In these patients, surgery could have been potentially avoided altogether if better diagnostic markers existed. In other patients, who undergo only partial thyroidectomy initially, a second surgery becomes necessary when thyroid cancer is confirmed. This group would benefit from markers that reliably indicated thyroid cancer at the outset, so that the appropriate extent of thyroid surgery could be accomplished at the first operation.<\/p>\n

It is no wonder that these suboptimal clinical scenarios inspired decades of investigation into potential molecular markers of thyroid cancer [4]. Several promising innovations have come to direct availability for patient care in the last few years, and they represent very different strategies. Some investigators focused on detecting known gene mutations (e.g. BRAF, RAS, PTC\/RET<\/em>) associated with thyroid cancer from the aspirated specimens in FNAB. This was pioneered by the work of Nikoforov and colleagues and acknowledged as a potential diagnostic tool in the American Thyroid Association 2009 guidelines for management of thyroid nodules and thyroid cancer [1,5]. In 2011, testing for these thyroid cancer-related mutations in FNAB became commercially available. Another group of investigators also focused on information obtained via FNAB samples, but developed a 142-gene profile that would classify the nodule as benign, potentially allowing surgery to be avoided or postponed. This effort was based on a multi-institutional study and acquisition of large sample cohorts, also leading to a commercially available product in 2011 [7, 8 and see this issue of CLi, page 14].<\/p>\n

In contrast to such tissue-based strategies, the TSHR mRNA molecular marker is derived from a peripheral blood test sample and was first available for routine testing in October 2008. It functions as a surrogate marker for circulating thyroid cancer cells, and is not detectable in individuals who have normal thyroid glands. As a blood test, it is convenient to obtain and can be measured at various time intervals, thus functioning both for initial diagnostic purposes and for later roles in prognosticating outcome from thyroid cancer surgery.<\/p>\n

In 2002, investigators at the Cleveland Clinic, USA, led by Dr Manjula Gupta first reported the method of detecting TSHR mRNA from peripheral blood samples of patients [9], [Figure 1]. It relied on the separation of mononuclear cells from the buffy coat layer, total RNA extraction and then RT-PCR using a patented primer pair that was found to be most effective in pre-clinical studies. In 2007, the assay technique switched to quantitative RT-PCR, defining a threshold level of TSHR mRNA >1 ng\/ug total RNA to indicate the presence of thyroid cancer [10]. This technique was estimated to have a sensitivity that detects fewer than ten thyroid cancer cells per one mL of blood. <\/p>\n

Studies that were conducted at the Cleveland Clinic since 2002 elucidated the following important aspects of TSHR mRNA [summarised in reference 11]. <\/p>\n