Management of follicular thyroid carcinoma should be individualised based on degree of capsular and vascular invasion
Introduction
Follicular thyroid cancer (FTC) is a relatively rare malignancy accounting for approximately 10–15% of cases of thyroid malignancy.1, 2 Despite being a distinct entity, FTC has often been studied together with the other subtypes of differentiated thyroid cancer, papillary thyroid cancer and Hürthle cell cancer.3, 4 Follicular thyroid cancer is, however, distinctive in that it infrequently metastasises to lymph nodes, more commonly presents with distant metastases5 and may have a less favourable prognosis when compared to papillary thyroid cancer.1, 6, 7
There is also considerable inter-observer variability in the histopathological diagnosis of FTC.8 In recent years the diagnosis of FTC has been refined with the exclusion of atypical follicular adenomas that may have previously been classified as minimally invasive FTC.2, 9 The subclassification of FTC into minimally invasive (MI FTC) and widely invasive (WI FTC) subtypes is well accepted, however, definitions of the extent of capsular invasion vary. Such variations in histopathological diagnosis make the comparison of different cohorts of patients difficult and compounds clinical uncertainty regarding prognosis.10, 11, 12, 13 Additionally, the influence of vascular invasion on prognosis remains controversial with some studies classifying a third group of FTC, angioinvasive MI FTC with a prognosis intermediate between MI FTC without vascular invasion and WI FTC.14, 15
The clinical implications of these subclassifications are important as they dictate treatment options.16 Some studies have reported a very small risk of recurrent disease or distant metastasis in patients with minimally invasive FTC8, 12, 17, 18, 19 and hence it has been suggested that in such patients hemithyroidectomy alone may be adequate treatment. In contrast other studies report distant metastasis in those with MI FTC20, 21, 22 and hence advocate total thyroidectomy and radioactive iodine remnant ablation in all patients with FTC. Other prognostic factors in FTC such as increasing age and increasing tumour size may also assist in individualising treatment regimes.23, 24, 25 The aim of this study was to review our experience with FTC and to quantify the risk of distant metastasis based on initial clinical and histopathological features. In particular we aimed to identify if there is a group of patients with FTC for whom hemithyroidectomy alone is sufficient treatment.
Section snippets
Identification and classification of patients
Patients with follicular thyroid cancer were identified from a prospectively maintained surgical database. Only patients with FTC confirmed at histopathological examination were included; those with Hürthle cell thyroid cancer and follicular variant papillary thyroid cancer were specifically excluded. All specimens were reported by a dedicated endocrine pathologist. A minimum of 10 tissue blocks were examined, including examination of the entire capsule. In equivocal cases, specimens were
Baseline clinical and pathological characteristics
Between January 1983 and December 2008, 124 patients with follicular thyroid cancer were identified and complete follow-up data was available in 122. Minimally invasive tumours were identified in 113 patients; vascular invasion was absent in 61 patients (Group 1, MI FTC) and present in 52 patients (Group 2, angioinvasive MI FTC). Eleven patients had widely invasive FTC (Group 3, WI FTC).
The baseline characteristics of these patients, details of treatment, histopathological features and
Pathological classification of follicular thyroid cancer
This manuscript documents our experience with follicular thyroid cancer over a 15-year period. Papillary thyroid cancer (including follicular variant papillary thyroid cancer) and Hürthle cell cancer were specifically excluded and patients were subclassified on the basis of capsular and vascular invasion. By this system of classification, the majority of patients had minimally invasive tumours with only 9% of patients in this series having widely invasive tumours. Although in other series, the
Conclusion
The prognostic factors of age, vascular and capsular invasion can be used in combination to individualise treatment, in particular to select patients who may be safely treated with less than total thyroidectomy and radioactive iodine remnant ablation. For patients aged ≤45 years with minimally invasive tumours without vascular invasion hemithyroidectomy alone may be adequate treatment. All other patients with follicular thyroid cancer should undergo total thyroidectomy and radioactive iodine
Acknowledgements
Dr C.J. O’Neill is supported by a grant from the NSW Cancer Institute.
A/Prof S.B. Sidhu is a New South Wales Cancer Institute Fellow.
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