Endocrine Abstracts

Introduction: Papillary thyroid cancer (PTC) is usually tied to an excellent prognosis, with a 10-year disease specific survival rate of 98%. Nevertheless, some clinicopathological features are associated with a worse outcome. Therefore, a precise risk assessment is crucial for the clinicians deciding the most appropriate treatment for each tumour. Multifocal tumours (MFPTC) appear to have be a worse prognosis than unifocal tumours (UFPTC) in some series, but this aspect is disregarded by the American Thyroid Association guidelines for risk stratification on PTC. The following study tries to evaluate a possible association between MFPTC and aggressive histopathological findings.

Material and Methods: We designed a retrospective cross-sectional observational study. Data regarding every histologically confirmed PTC (non-aggressive variants) larger than 2 mm operated at our centre between 2001 and 2019 was gathered. We used chi square test to evaluate the association between multifocality and several aggressive histopathological findings: extrathyroidal extension (ETE), lymph node involvement (LNI), BRAFV600E mutation and desmoplastic stromal reaction.

Results: We studied 662 patients with non-aggressive variants of PTC. 651 patients had the ETE described in their pathological reports: 404 UFPTC (19.6% with ETE) and 247 MFPTC (26.3% with ETE). From 639 patients, there were LNI in 170 histological specimens:35.8% of MFPTC (88 out of 246) and 20.9% of UFCPT (82 out of 392). 344 neoplasms had been tested for BRAF V600E mutation: 200 UFPTC (46.5% mutated) and 144 MFPTC (57.6% mutated). In 524 patients the presence or absence of desmoplastic reaction was described in their pathological reports: 308 UFPTC (34.7% with moderate to severe desmoplasia) and 216 MFPTC (46.3% with moderate to severe desmoplasia). There were no differences between groups in sex distribution, age nor tumour size (used largest focus of MFPTC). There was a statistically significant association between the following: MFPTC and ETE [P = 0.04, OR (CI95%) = 1.47 (1.01–2.14)]; MFPTC and LNI [P < 0.0001, OR (CI95%) = 2.11 (1.48–3.02)]; MFPTC and the presence of BRAFV600E mutation [P = 0.04, OR (CI95%) = 1.56 (1.02–2.41)]; and MFPTC and moderate to severe desmoplastic reaction [P < 0.01, OR (CI95%) = 1.62 (1.14–2.31)].

Conclusion: MFPTC are associated with several aggressive histopathological findings:ETE, LNI, BRAF V600E mutation and moderate to severe desmoplasia. Therefore, we suggest that multifocality should be regarded when deciding the treatment of PTC, aiming for more extensive surgical treatment when multifocality is present. The association between MFPTC and aggressive histopathological findings questions the currently proposed surgical approach for intrathyroidal PTC smaller than 4 cm (lobectomy) due to the risk of neglecting evidence of multifocality.