Endocrine Journal
Online ISSN : 1348-4540
Print ISSN : 0918-8959
ISSN-L : 0918-8959
CASE REPORT WITH REVIEW OF LITERATURE
A case report of anaplastic thyroid carcinoma transformed from small papillary carcinoma successfully detected by ultrasonography in its early stage with review of literature
Hiroshi Arimitsu, Yui Nishijima, Naoyuki Higaki, Hitoshi Noguchi, Shinya Uchino, Tsukasa Murakami
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Keywords: Papillary microcarcinoma, Anaplastic thyroid carcinoma, Ultrasonography, Fine-needle aspiration cytology
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2023 Volume 70 Issue 11 Pages 1097-1101

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Abstract

An 82-year-old woman was referred to our hospital because of a suspicious thyroid nodule. She was diagnosed with papillary microcarcinoma with a maximum diameter of 9 mm based on ultrasonography and fine-needle aspiration (FNA) cytology. She preferred observation without surgery. Her papillary carcinoma grew gradually and reached a maximum diameter of 19 mm after 23 months. At that time, ultrasonography showed an apparent change in the shape of the nodule as well as in its diameter. At the initial ultrasound examination, papillary microcarcinoma was demonstrated as a hypoechoic solid nodule with an irregular shape. No punctuate microcalcifications were shown. After 23 months, the preexisting nodule had expanded toward the common carotid artery. The expanded portion was round and well demarcated. FNA revealed that the expanded portion consisted of anaplastic thyroid carcinoma. She underwent hemithyroidectomy and lymph node dissection of the central compartment. She remained in good health for 18 months after surgery. Anaplastic thyroid carcinoma is generally found as an aggressive large tumor, and the ultrasound appearance of small anaplastic thyroid carcinoma is poorly understood at present. We successfully detected anaplastic transformation in the early period by ultrasonography and FNA. When observation is indicated for small papillary thyroid carcinoma, the change in the shape of the nodule as well as in its diameter should be carefully monitored by ultrasonography. FNA should be performed at a proper site on the nodule to avoid overlooking anaplastic transformation, as resection following the early detection of anaplastic transformation might bring a favorable prognosis.

PAPILLARY THYROID CARCINOMA (PTC) comprises approximately 90% of all thyroid malignancies and has a good prognosis. In particular, PTCs with a maximum diameter of ≤10 mm have an extremely favorable prognosis. Ito et al. reported that the incidence rate of size enlargement after 10 years of observation was 8.0% among 1,235 patients with papillary microcarcinoma (PMC) [1]. Active surveillance without immediate surgery for low-risk PMC has been adopted as a feasible strategy [2, 3]. However, anaplastic thyroid carcinoma (ATC) has an extremely poor prognosis. Since some ATCs are known to arise from preexisting PTC, overlooking transformation to ATC should be avoided.

We recently successfully detected anaplastic transformation in a patient with PMC by close observation by ultrasonography. Observation of the change in shape as well as in the diameter of the carcinoma is essential. Fine-needle aspiration (FNA) at the proper site of the nodule is also required for the early detection of anaplastic transformation.

Case Presentation

An 82-year-old woman was referred to our hospital because of a suspicious thyroid nodule. Her thyroid nodules had been observed for the past 15 years by her family doctor, who also managed her chronic kidney disease. Ultrasonography of the neck revealed several thyroid nodules, and 1 with a maximum diameter of 9 mm located in the right lobe was suspected of being PTC because of its irregular shape, hypoechogenicity and suspicious extrathyroid extension (Fig. 1). The diagnosis of PTC was confirmed with FNA cytology (Fig. 2). She had no distant metastases and no lymph node metastases. Thyroidectomy was proposed, but she elected to receive observation without surgery due to concerns about the deterioration of her chronic kidney disease. Her estimated glomerular filtration rate (eGFR) was 10.6 mL/min/1.73 m2 at the first visit to our hospital.

Fig. 1

Transverse scan of the right lobe of the thyroid at the first visit. An irregular-shaped hypoechoic solid nodule is demonstrated. The thyroid capsule seems to be interrupted by tumor extension. The maximum diameter of the nodule was 9 mm. CCA: common carotid artery, T: trachea, arrow: site of aspiration for the cytological examination.

Fig. 2

Fine-needle aspiration cytology revealed tumor cells overlapping irregularly. Powdery chromatin and nuclear grooves were shown. Papanicolaou stain, ×40.

Hemodialysis was conducted one year later. She was observed carefully by ultrasonography every three to five months. Although her PTC gradually increased in diameter, she still preferred to continue observation. At 23 months after the first visit, we detected apparent changes in the shape of her PTC. The nodule had expanded toward the common carotid artery, and the expanded portion was clearly demarcated from the surrounding tissues and round-shaped (Fig. 3), which differed from previous ultrasonograms of preexisting PTC. Finally, ATC was confirmed with an FNA sample obtained at the expanded portion (Fig. 4).

Fig. 3

Transverse scan of the right lobe of the thyroid at 23 months after the first visit. A nodule expanding towards the common carotid artery in addition to the preexisting papillary carcinoma was demonstrated. The maximum diameter of the nodule was 19 mm. CCA: common carotid artery, T: trachea, asterisk: preexisting papillary carcinoma, arrow: site of aspiration for cytological examination.

Fig. 4

The nuclei of tumor cells are highly pleomorphic. Mitotic cells were observed. Papanicolaou stain, ×40.

Hemithyroidectomy and dissection of the lymph nodes in the central compartment were performed immediately. Her cancers were successfully resected without any postoperative complications. Macroscopic and microscopic specimens are shown in Figs. 5 and 6. The resected tumor consisted of PTC and ATC. The diameter of the ATC was 14 mm. Immunohistochemical staining of the ATC revealed positive findings for TTF-1, BRAFV600E and TP53 but negative findings for thyroglobulin. In the 18 months since the operation, no recurrence of ATC was found, and she remained in good health on hemodialysis.

Fig. 5

Macroscopic view of the resected specimen. The cut surface of the papillary thyroid carcinoma is whitish, while that of anaplastic thyroid carcinoma is grayish and contains hemorrhagic foci.

Fig. 6

Microscopic specimen showing papillary thyroid carcinoma (A) and anaplastic thyroid carcinoma (B). H-E stain, ×10. Both carcinomas are shown in (C). H-E stain, ×4.

Discussion

ATC is an aggressive tumor that grows rapidly, becoming a large tumor infiltrating the surrounding tissues. Therefore, curative resection at the first presentation of the tumor is often difficult. Distant metastases are found in some patients. Sugitani et al. reported that the 6-month and 1-year cause-specific survival rates for 547 patients with ATC were 36% and 18%, respectively, in 2012 [4]. Another recent large-scale observation [5] revealed that the median overall survival (OS) for 477 patients with ATC was 0.79 years (9.5 months), ranging from 0.01 to 16.63 years. The 6-month, 1-year, and 2-year OS rates were 67% (95% confidence interval [CI], 63%–71%), 44% (95% CI, 40%–49%), and 25% (95% CI, 21%–29%), respectively. Factors associated with an improved prognosis are targeted therapy and immunotherapy. It is also known that the prognosis is better when ATC can be resected [5-8]. While the prognosis of ATC has improved recently, it is still significantly poorer than that of differentiated thyroid carcinomas (DTCs).

In this case report, we showed an ultrasonogram of a small ATC that was successfully detected during careful observation of a PTC. Ultrasound appearances of such a small ATC have not been well elucidated. It appeared as a round, hypoechoic solid nodule, and the margin was well demarcated, which differed substantially from that of the preexisting PTC. It also differed from the ultrasonic characteristics of the ATC previously reported by Hahn et al. [9] and Gu et al. [10]. As ATC is usually a large tumor, imaging is mainly performed via computed tomography (CT) [11-13]. Therefore, reports of the ultrasound appearance of ATC are limited. Hahn et al. [9] reported the ultrasound findings of 26 ATCs with a mean tumor size of 4.2 cm. Gu et al. [10] described the ultrasound findings of 15 ATCs with a mean tumor size of 5.8 cm. Many ATCs appear as irregularly shaped, poorly circumscribed, large tumors. The internal echotexture is hypoechoic and heterogeneous. Calcification was detected in 54%–80% of the tumors.

Active surveillance without immediate surgery is a well-established strategy for the management of low-risk PMC [14-16]. Tumor enlargement was reportedly observed in 8.0% of 1,235 patients with PMC after 10 years of observation [1]. As active surveillance, ultrasonography should be conducted to detect increases in the maximum diameter of the nodule, the development of lymph node metastases and extrathyroidal extension [1, 14-16]. However, changes in the characteristics of the nodule, such as the shape, should also be evaluated carefully. These changes might reflect changes in the nature of the nodule itself. The nodule in our patient gradually increased in diameter and finally showed apparent changes in its shape. Although no patients with anaplastic transformation during active surveillance of PMC have been reported thus far, even in large-scale observations and meta-analyses [17-19], FNA should be considered for growing and changing portions in such situations.

The mechanism underlying the transformation of PTC to ATC is considered to involve the accumulation of mutations in several oncogenes or tumor suppressor genes [20, 21]. One of the risk factors for ATC is preexisting DTC [22]. Old age and long-standing multinodular goiter are also known to be risk factors for ATC [23]. In addition, Oishi et al. reported that a TERT promoter mutation in PTC is an independent risk factor for anaplastic transformation [24]. However, it is impossible to predict transformation to ATC based on clinical findings. To our knowledge, there have been no reports of the rate of anaplastic transformation from PTC. However, the incidence rates of ATC and PTC are reported to be 0.12 and 10.65 per 100,000, respectively [25]. Taking the indolent nature of PTC into consideration, the rate of anaplastic transformation is presumed to be extremely rare. Although anaplastic transformation is a rare event, close attention should be given when conducting observation of PTC in elderly patients.

We described a patient with a small ATC arising from preexisting PTC. Ultrasonography demonstrated a small ATC that apparently differed from known ultrasound images of ordinary ATC. The lesion was successfully resected, and the patient has been in good health for 18 months since the operation. A delayed diagnosis of ATC should be avoided, as curative resection can improve the prognosis. Careful ultrasound observation, including monitoring the change in shape as well as in the diameter, and FNA at the proper site are mandatory in such cases.

Disclosure

Tsukasa Murakami is a member of Endocrine Journal’s Editorial Borad. None of the authors have any potential conflicts of interest associated with this research.

References
 
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