Propensity analysis reveals survival disparities between T1a and T1b well-differentiated thyroid cancer based on surgery.

Background: With rising well-differentiated thyroid cancer (WDTC) incidence, the appropriate treatment choice remains controversial for T1 tumors <2 cm. This study analyzed differences in surgery refusal and survival outcomes between T1a (<1 cm) and T1b (1-2 cm) WDTC, examining the demographic and clinical characteristics associated with patients who decide to either undergo or refuse recommended surgery.

Methods: We studied 81,664 T1N0M0 WDTC patients in the Surveillance, Epidemiology, and End Results (SEER) registry [2000-2019]. Treatment with surgery (n=81,565) or refusal (n=99) was compared. Propensity score matching balanced groups. Cox models assessed mortality predictors.

Results: Among 81,664 patients, the overall mortality rate was 5.7% (n=4,635 deaths). Refused surgery associated with higher mortality (11.1% . 5.7%, P=0.03) and shorter survival times (152.05±7.43 . 178.62±0.17 months, P<0.001). Thyroid cancer-specific mortality rates were 2.2% for refused surgery and 0.4% with surgery (P=0.01). Refusing surgery carried over twice the mortality risk [adjusted hazards ratio (aHR) =2.15, 95% confidence interval (CI): 1.01-4.57, P=0.046]. However, for T1b patients, refusing surgery escalated mortality risk over 3-fold (aHR =3.44, 95% CI: 1.43-8.28, P=0.006), yet for T1a patients it showed no increased risk (aHR =0.41, 95% CI: 0.049-3.46, P=0.42). Other independent risk factors for mortality included older age (aHR =6.24 for ≥55 years) and prior malignancy (aHR =2.78).

Conclusions: Our study reveals notable differences in survival and mortality between T1a and T1b WDTC, underscoring the need for subtype-specific, evidence-based treatment guidelines. For T1b patients, surgery remains the standard of care with significant improvements in outcomes. In contrast, select T1a patients may benefit from active surveillance, offering comparable survival rates while potentially enhancing quality of life.