Poorly Differentiated Thyroid Cancer—Still a Clinical Dilemma: A Case Study

INTRODUCTION

Poorly differentiated thyroid cancer (PDTC) is a rare disease. This is a clinically significant entity because, this causes most deaths from non-anaplastic follicular cell-derived thyroid cancer. The rarity of the disease and heterogeneous diagnostic criteria has been a reason there are limited studies on the diagnosis and management of PDTC. The presentation of PDTC patients is with adverse clinicopathologic characteristics: predominantly in old age males with advanced disease, and distant metastases. In management, part surgery with strict adherence to oncological principles can eradicate loco-regional disease. However, there is a large number of PDTC patients with distant metastatic disease which causes death in most patients.

CASE DESCRIPTION

The patient was a 73 years old female who presented with an enlarging neck swelling predominantly right side for the past eight years. The patient did not have any other complaints other than neck swelling (Fig. 1). The patient had already undergone hemithyroidectomy 40 years ago but the reasons and the tissue diagnosis were not available.

The patient had a large goiter predominantly right lobe enlargement, mobile with deglutition, firm in consistency with no signs of hyper or hypothyroidism. No significant cervical lymphadenopathy.

Pre-op workup revealed a normal thyroid function test. MRI neck showed a heterogeneous lesion arising from the right lobe of the thyroid with no retrosternal extension (Fig. 2). However, the lesion had a mass effect on the trachea causing luminal narrowing (Fig. 3) and a few subcentimetric nonspecific lymph nodes were identified. Features were likely representing long-standing dominant nodules of multinodular goiter. Fine needle aspiration (FNA) was done and impression was inconclusive (DD: 1. Dominant nodule, 2. Follicular neoplasm).

After optimization and anesthesia fitness, the patient underwent completion thyroidectomy. Postoperative period was uneventful.

Postoperative histopathology reports revealed poorly differentiated thyroid carcinoma with a microscopic focus on radial margin invasion (Figs 4 to 6). The patient was reviewed twice and then defaulted for follow-up.

DISCUSSION

The terminology poorly differentiated thyroid carcinoma was introduced in 1963 by Granner et al. Though introduced way back these tumors were classified as conventional follicular carcinomas as they can form follicles. It was not recognized as a separate entity until 2004 when World Health Organization (WHO) classified it as a separate entity in the classification of endocrine tumors.¹ This classification placed the PTDC in the intermediate zone in the spectrum of differentiated thyroid cancer (DTC) and ATC.

Prevalence of PTDC varies from 2 to 15%.² Origin of PTDC may be de novo or from DTC. The median age of incidence is around 59 years. Females are affected more commonly than males with an incidence ratio (female to male ratio) of 1.6:1.³ Moreover, in 50% of the cases, there is extra thyroidal spread at the presentation itself. Regional lymph node metastasis is 50–85% in PDTC of cases but it is only 40–75% in differentiated thyroid cancer.^2,4 The distant metastasis percent is quite higher in PDTC at 85%, which is 10–33% in DTC.^5,6

Though accepted as a separate entity, there have been differences of opinion in diagnosis. The pathologists had trouble agreeing on the histopathological features of PTDC. Solid or trabecular pattern alone was relied upon by some pathologists. The Memorial Sloan Kettering Cancer Center (MSKCC) made a proposal. They didn’t take architectural growth pattern into consideration and defined diagnostic criteria of PDTC by relying only on the mitotic index (≥5 mitosis/10 HPF (400 ×) and evidence of necrosis in a tumor having follicular differentiation proved either on HPE or immunohistochemistry.

Later in 2006, Turin’s proposal incorporated both the characteristics into diagnosis criteria.⁷ This provided the current diagnostic criteria. The criteria are: 1) growth pattern (solid/trabecular/insular); 2) nuclear features of papillary thyroid carcinoma should not be present; 3) at least one of the following three features: mitotic index ≥3/10 HPFs, tumor necrosis, convoluted nuclei. World Health Organization classification adopted both architecture and high-grade tumor features, which implies an undifferentiated (non-follicular and non-papillary) pattern of growth, a high mitotic index, invasive growth, and necrosis.⁸ World Health Organization classification of endocrine tumors took Turin criteria into account.⁹

There is no clear protocol for disease management of PDTC. Treatment of PDTC is approached with the knowledge gained from experience in the management of DTC. Initial surgery with oncological principles is important for locoregional disease control in PDTC (total thyroidectomy). If there are any suspicious nodes, central, functional neck dissection can be carried out (five-year locoregional control in up to 81% of PDTC.² Adjuvant treatment benefits are inconclusive.

No modalities of adjuvant therapy have been shown to be efficient in PDTC. Radioactive iodine (RAI) avidity of PDTC is variable.¹⁰

Whether the disease is local or has already metastasized PDTC shows an aggressive course, when compared with DTC.¹¹ Complete clearance of the gross disease provides satisfactory 5-year loco-regional control. Control of distant metastasis is low (59% over 5 years) with the most common metastasis in the lung and bone. About 85% of the deaths in PDTC are due to metastatic disease.³

CONCLUSION

We lost follow-up of the patient and couldn’t report the current status. Systematic approach guidelines should be made available for poorly differentiated thyroid carcinoma. This helps the medical team in taking care of patients with this type of disease, as we lack literature that provides conclusive evidence because it is a novel member of thyroid cancers. There is no available therapy to control the systemic spread of the disease. The future lies in the targeted therapy that will lead us to better management of the disease.

ORCID

Raju Palanigoundar https://orcid.org/0009-0006-7584-1674

Karthikeyan Raju https://orcid.org/0009-0004-2440-6643

Archana Harikrishnan https://orcid.org/0009-0008-5294-3381

Senthil Kumar https://orcid.org/0009-0007-0434-3835

Sabarigirivasan Kumba Santharam https://orcid.org/0000-0001-7302-1177

REFERENCES

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