Follicular thyroid carcinoma: the role of histology and staging systems in predicting survival.
OBJECTIVE
To evaluate the risk factors including tumor histomorphology for survival specific to follicular thyroid carcinoma (FTC) and to apply commonly employed staging systems in predicting survival for patients with FTC.


BACKGROUND
FTC is usually analyzed collectively with papillary thyroid carcinoma (PTC) in risk group analysis. Risk factors and risk group analysis are important in the management of patients with FTC, although current published therapeutic guidelines call for total thyroidectomy followed by radioactive iodine (I) ablation for all FTC patients.


METHODS
Over a 40-year period, 156 patients surgically treated for FTC with an average follow-up of 14.4 years were retrospectively studied after histologic reclassification according to the type and degree of invasiveness of the tumor. Potential risk factors for survival were calculated using multivariate analysis, and the prognostic accuracy of AMES risk group stratification, UICC/AJCC pTNM staging, Degroot classification, and MACIS scoring schemes in predicting survival was compared.


RESULTS
Seventeen (11%) patients had distant metastases at presentation, and bilateral thyroid resection was performed for 131 (84%) patients. Seventeen (11%) patients died of recurrent or metastatic disease. The overall and cancer-specific survival (CSS) rates at 10 years were 79% and 88%, respectively. None of the patients with minimally invasive (n = 49) or angioinvasive (n = 23) carcinomas died compared with 17 of 84 patients with widely invasive carcinomas (P = 0.0007). Using the Cox proportional hazards model, old age, the presence of distant metastases, and incomplete tumor excision were independent prognostic factors for survival. For patients who underwent curative treatment, old age and widely invasive carcinoma were risk factors for poor survival. All staging systems studied accurately predicted CSS, and the pTNM UICC/AJCC staging system yielded the best prognostic information.


CONCLUSIONS
Commonly adopted staging systems can be applied specifically to patients with FTC. The distinction of FTC in minimally invasive and widely invasive carcinoma based on the extent of invasiveness rather than vascular invasion is important in identifying low-risk FTC patients for a more conservative management.
Lo
Chung-Yau
CY
Departments of Surgery, University of Hong Kong Medical Centre, Queen Mary Hospital, Pokfulam, Hong Kong, China. cylo@hkucc.hku.hk
Chan
Wai-Fan
WF
Lam
King-Yin
KY
Wan
Koon-Yat
KY
D018263:Adenocarcinoma, Follicular / Q000401:mortality* / Q000473:pathology* / Q000601:surgery; D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D001707:Biopsy, Needle; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D009361:Neoplasm Invasiveness / Q000473:pathology*; D009367:Neoplasm Staging / Q000592:standards*; D011237:Predictive Value of Tests; D011336:Probability; D011379:Prognosis; D016016:Proportional Hazards Models; D012189:Retrospective Studies; D018570:Risk Assessment; D012737:Sex Factors; D016019:Survival Analysis; D013964:Thyroid Neoplasms / Q000401:mortality* / Q000473:pathology* / Q000601:surgery; D013965:Thyroidectomy / Q000379:methods; D016896:Treatment Outcome