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Prognostic Factors in Papillary and Follicular Thyroid Carcinoma: Their Implications for Cancer Staging

¹ Division of Endocrine Surgery, Department of Surgery, University of Hong Kong Medical Centre, Queen Mary Hospital, 102 Pokfulam Road, Hong Kong SAR, China
² Discipline of Pathology, School of Medicine, Griffith University, Gold Coast, Australia
³ Department of Clinical Oncology, University of Hong Kong Medical Centre, Queen Mary Hospital, Pokfulam road, Hong Kong SAR, China

Correspondence: Address correspondence and reprint requests to: Chung-Yau Lo, MS, FRCS (Edin), FACS; E-mail: cylo{at}hkucc.hku.hk

Background: Papillary thyroid carcinoma (PTC) and follicular thyroid carcinoma (FTC) are two distinct histological types of thyroid carcinoma but have often been studied and staged as a collective group, known as differentiated thyroid carcinoma (DTC). However, this may not be an optimal approach to cancer staging.

Methods: A total of 760 patients with DTC, comprising 589 (77.5%) with PTC and 171 with (22.5%) FTC, being managed at our institution from 1961 to 2001 were retrospectively reviewed. Their clinicopathological features, treatment modalities received, and postoperative outcome were analyzed. Both univariate and multivariate analyses were performed to identify prognostic factors related to cancer-specific survival (CSS) for PTC and FTC.

Results: There were statistically significant differences between PTC and FTC in terms of age 50 years at diagnosis (P = .040), tumor size (P < .001), lymph node metastases (P < .001), distant metastases (P < .001), extrathyroidal extension (P < .001), multifocality (P = .002), capsular invasion (P < .001), extent of thyroid resection (P < .001), radioiodine ablation (P < .001), and external-beam irradiation (P = .003). Although PTC and FTC had similar 10-year and 15-year CSS (P = .846), each possessed its own set of independent prognostic factors for CSS. Age at diagnosis and completeness of resection were independent prognostic factors in both PTC and FTC.

Conclusions: There were marked differences in clinicopathologic features, treatment, and prognostic factors between the two histologic types of DTC. Different staging systems should be evaluated and validated for PTC and FTC individually in the future.

Key Words: Prognostic factors • Differentiated thyroid carcinoma • Papillary thyroid carcinoma • Follicular thyroid carcinoma • Staging • Risk stratification

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