Outcomes of papillary thyroid microcarcinoma presenting with palpable lateral lymphadenopathy.

Purpose-Papillary Thyroid Microcarcinoma(PTMC) is typically indolent, allowing management with active surveillance(AS) protocols. Occasionally, a more aggressive phenotype can present and may lead to poor outcomes such as patients presenting with clinically significant lateral lymphadenopathy(cN1b). Prior analysis of the outcomes of this cohort is largely from PTC(>1cm) or from institutions where use of radioactive iodine(RAI) is limited. Hence, we aim to describe the outcomes of patients with PTMC who presented with palpable cN1b disease, treated with total thyroidectomy and RAI. Methodology-We performed a retrospective cohort study. Outcomes of patients with PTMC who presented with palpable lateral lymph node metastases(microPTCcN1b) treated between 1997-2020 at Royal North Shore Hospital were compared to two control groups' outcomes; patients with clinically detected PTMC without evidence of involved lymph nodes(microPTCcN0), and with larger PTC(>10mm) who presented with palpable lateral lymphadenopathy(larger PTCcN1b). We assessed clinicopathological variables, post-operative risk-stratification, disease recurrence, re-operative surgery, and structural disease-free survival. Results-In total, 1534 PTMCs were diagnosed following thyroid surgery in the study period; of these, 157(10%) were clinically detected microPTCcN0 and 26 microPTCcN1b(1.7%). There were 138 patients in the larger PTCcN1b control group. All cN1b patients were treated with total thyroidectomy and adjuvant RAI. Mean size of the largest lymph node deposit was similar between the microPTCcN1 and larger PTCcN1 groups(23versus27mm,p=0.11). Patients with microPTCcN1 were more likely to have biochemical or structural persistence or recurrence compared to microPTCcN0(19%,5/26versus3.8%,6/157,p=0.002), but less likely than larger PTCcN1b patients(19%,5/26versus42%,58/138,p=0.04). All patients in the microPTCcN1b group who had an excellent response to initial therapy(85%,22/26) were disease-free at last follow-up. The rate of re-operation was similar for the microPTCcN1b and microPTCcN0 groups(4%,1/26versus2%,3/157,p=0.461), and significantly lower than the larger PTCcN1b group(4%, 1/26 versus 26%,36/138,p=0.002). Five-year disease-free survival estimates were significantly better for microPTCcN1b patients than larger PTCcN1b patients(94%versus59%,p=0.001). Conclusion-MicroPTCcN1b patients treated with thyroidectomy and adjuvant RAI have inferior clinical outcomes compared with microPTCcN0 patients, but have better outcomes than their larger PTCcN1b counterparts with respect to disease persistence and recurrence. Response to initial therapy provides valuable prognostication in microPTCcN1b patients: if these patients had an excellent response to initial treatment, they achieved long-term disease-free survival in this series.