Encapsulated Angioinvasive Follicular Thyroid Carcinoma: Prognostic Impact of the Extent of Vascular Invasion

Role of the Degree of Vascular Invasion in Predicting Prognosis of Follicular Thyroid Carcinoma

OBJECTIVE

The present study investigated the prognostic factors for follicular thyroid carcinoma (FTC) with the incorporation of the histologic subtype and degree of vascular invasion (VI).

PATIENTS

The records of 474 patients with FTC confirmed by surgical specimens at Ito Hospital from January 2005 to December 2014 were reviewed in this retrospective cohort study. The Cox proportional hazard model was used to determine factors associated with disease-free survival (DFS) and distant metastasis-free survival.

RESULTS

Of the 474 patients, 140 (30%) had minimally invasive FTC, 260 (55%) had encapsulated angio-invasive FTC, and 74 (16%) had widely invasive FTC. Among the 428 patients with M0 FTC, the 10-year DFS rates of patients with minimally invasive FTC (n = 133), encapsulated angio-invasive FTC (n = 247), and widely invasive FTC (n = 48) were 97.3%, 84.2%, and 69.9% (P < .001), respectively. A multivariate analysis identified aged ≥55 years (hazard ratio [HR], 2.204; 95% CI, 1.223-3.969; P = .009), histologic subtype (HR, 2.068; 95% CI, 1.064-4.021; P = .032), VI of ≥2 (HR, 6.814; 95% CI, 3.157-14.710; P < .001), and tumor size >40 mm (HR, 2.014; 95% CI, 1.089-3.727; P = .026) as independent negative prognostic factors for DFS.

CONCLUSION

Our study results may enable us to stratify the prognosis of FTC more accurately by combining the histologic subtype with the degree of VI ≥2, aged ≥55 years, and tumor size >40 mm.

New Insights on the Importance of the Extent of Vascular Invasion in Widely Invasive Follicular Thyroid Carcinoma

BACKGROUND

This study aimed to investigate the association between the extent of vascular invasion (VI) and the outcome of widely invasive follicular thyroid carcinoma (WI-FTC).

METHODS

The records of 107 patients with WI-FTC confirmed by surgical specimens from January 2005 to December 2016 were retrospectively reviewed.

RESULTS

Among the 107 patients with WI-FTC, those with a VI of < 4 (n = 62) and ≥ 4 (n = 45) had a 10 year cause-specific survival (CSS) rate of 97.7% and 89.4% (p = 0.008), respectively. Univariate analysis identified M1 (p = 0.001), and the number of VI of ≥ 4 as significant negative prognostic factors for CSS. Multivariate analysis identified M1 (hazard ratio [HR] = 9.366) as independent negative prognostic factor for CSS. Among the 72 patients with M0 WI-FTC, those with a VI of < 2 (n = 33) and ≥ 2 (n = 39) had a 10-year distant metastasis-free survival (DMFS) rate of 96.8% and 56.8% (p = 0.001), respectively. Univariate analysis identified age ≥ 55 years (p = 0.011), presence of VI, the number of VI of ≥ 2, and resection margin status (p < 0.001) as significant negative prognostic factors for DMFS. Multivariate analysis identified the number of VI ≥ 2 (HR = 9.137), and resection margin status (HR = 5.853) as independent negative prognostic factors for DMFS.

CONCLUSIONS

It may be unnecessary that WI-FTC with curative resection margin status and a VI of < 2, especially in capsular invasion only, routinely undergo completion thyroidectomy and postoperative ablation.

The Prognostic Impact of Extent of Vascular Invasion in Follicular Thyroid Carcinoma

BACKGROUND

Encapsulated angioinvasive follicular thyroid carcinoma (EAFTC) is associated with an increased risk of distant metastasis and reduced survival compared to minimally invasive follicular thyroid carcinoma (MIFTC). There is controversy regarding the extent of surgery and adjuvant radioactive iodine therapy for angioinvasive follicular thyroid carcinoma when stratified by number of foci of angioinvasion.

METHODS

All follicular thyroid carcinoma cases from 1990-2018 were identified from a thyroid cancer database. Primary outcomes were distant metastasis-free survival (DMFS) and disease-specific survival (DSS) with factors of interest being age, gender, tumour size, treatment, foci of angioinvasion and histological subtype.

RESULTS

A total of 292 cases were identified; 139 MIFTC, 141 EAFTC and 12 widely invasive follicular thyroid carcinoma (WIFTC). Over a follow-up period of 6.25 years, DMFS was significantly reduced (p < 0.001) with 14.2% (EAFTC) and 50% of WIFTC developing metastasis. The risk of metastasis in EAFTC with ≥ 4 foci of angioinvasion was 31.7% (HR = 5.89, p = 0.004), 6.3% for EAFTC with < 4 foci of angioinvasion (HR = 1.74, p = 0.47), compared to 3.6% MIFTC. Age ≥ 50 years (HR = 4.24, p = 0.005) and tumour size (HR = 1.27, p = 0.014) were significantly associated with increased risk of distant metastasis. DSS was reduced significantly (p < 0.001), with 7.8% EAFTC patients dying of disease. For EAFTC patients, DSS was 96.8% for < 4 foci and 82.6% for ≥ 4 foci of angioinvasion (p = 0.003).

CONCLUSION

EAFTC is at increased risk of distant metastasis related to the extent of angioinvasion. Tumours with < 4 foci of angioinvasion should be considered for a total thyroidectomy, particularly in older patients.

Prognostic factors for follicular thyroid carcinoma: the importance of vascular invasion

The World Health Organization (WHO) classifies follicular thyroid carcinoma (FTC) into three categories: minimally invasive (mFTC), encapsulated angioinvasive (eaFTC), and widely invasive (wFTC). This study investigated whether this classification is appropriate. We enrolled 523 patients who underwent initial surgery at Kuma Hospital between 1998 and 2015 and were diagnosed with FTC. Capsular invasion (CI) was classified as none, minimal (microscopic), or wide (macroscopic) invasion. Vascular invasion (VI) was divided according to the number of invasive foci into three degrees: VI(-), VI(1+), and VI(2+). For 507 M0 patients, age ≥55 years (p = 0.004), non-oxyphilic histology (p = 0.043), and male sex (p < 0.001) predicted poor distant recurrence-free survival (DR-FS) on univariate analysis; however, tumor size >4 cm and wide CI did not. The DR-FS rates significantly decreased from VI(-) to VI(2+) in a step-by-step fashion, including VI(-) vs. VI(1+) (p = 0.011) and VI(1+) vs. VI(2+) (p = 0.014). Multivariate analysis revealed that older age (p = 0.0004), non-oxyphilic histology (p = 0.041), male sex (p = 0.0052), VI(1+) (p = 0.017), and VI(2+) (p < 0.001) independently predicted distant recurrence. The DR-FS rates did not significantly differ among mFTC, wFTC/VI(-), and eaFTC/VI(1+). The DR-FS rate of eaFTC/VI(2+) was worse than that of eaFTC/VI(1+) (p = 0.042), but did not differ from that of wFTC/VI(1+/2+). Our findings suggest that subclassifying eaFTC according to the degree of VI and restricting wFTC to VI-positive cases would be better in the WHO classification. Revising the definition for wide CI is recommended.