Utility of Minimally Invasive Treatment for Papillary Microcarcinoma, Acknowledging Most Require No Treatment at All

Awareness of any new cancer invokes both fear and anxiety, in patients and clinicians alike. But it is well established that many small (< 1 cm), well-differentiated (papillary) thyroid cancers exist in an indolent and nonprogressing state. Screening studies confirm that many patients with no known thyroid illness harbor such indolent lesions (1), whereas postmortem identification of microcarcinomas is even more telling (2). But in contrast, a minority of small thyroid carcinomas can nonetheless prove dangerous, and logic also holds that aggressive or larger lesions must have been small at some point in their evolution. It is with this background that investigators have sought broader medical understanding of 2 important questions: Which thyroid cancers can be observed without intervention while maintaining a high degree of patient safety? And, when intervention is favored, what options exist to effectively and safely treat small thyroid cancers separate from surgical intervention?

In response to the latter question, the data by Yue and colleagues (3) provide important insight into the ability of minimally invasive (nonsurgical) interventions to be added to our armamentarium of care. In their study of 119 patients with micropapillary thyroid carcinomas (mPTCs), the authors demonstrate the effectiveness and safety of ultrasound-guided microwave ablation (UG-MWA) over a 3-year period. For these patients with low-risk and isolated mPTC, a 2-minute ablative procedure (at times repeated), preceded by only local anesthetic and well tolerated, can completely destroy nearly 80% of such carcinomas within a 15-month period. Hoarseness may occur in 7% of cases but is transient in nature and recovers within 2 to 3 months. For the remaining patients, only modest signs of the intervention such as necrosed or calcified remnant persist. From this, we can conclude that when performed by a trained physician in a structured and well-described fashion, the safety of MWA is apparent.

Furthermore, these data also demonstrate the efficacy of UG-MWA for treating mPTCs. No cases of apparent dangerous or distant metastatic spread occurred during the 3-year average follow-up duration (with some individuals followed > 8 years). Just one cervical lymph node metastasis was confirmed in a single patient (< 1%), which was amenable to treatment. UG-MWA treatment, not dissimilar to ethanol ablation or cryoablation, effectively destroys small-volume thyroid cancer with high certainty. Nonetheless, these data also confirm that even in these small thyroid carcinomas there exists a very low proportion of subclinical residual disease that can also recur and spread locally. For these rare scenarios, however, rescue surgery is able to address such findings with no apparent downstream consequence. Together, this long-term safety and efficacy analysis by Yue and colleagues provides clear and transparent data demonstrating that UG-MWA is a viable treatment option. Long-term data using sterile ethanol injection as another means of treatment in this setting have demonstrated similar findings (4).

Left unanswered is the question of when such a treatment option is actually needed. Asked differently, can most mPTCs simply be watched without any intervention whatsoever? Answers to these questions are quickly evolving, but certainly require more investigation. Ito, Miyauchi, and team members from Japan first demonstrated that carefully selected (low-risk) mPTCs could be safely monitored for years without surgery or other intervention (5). Over time, most such thyroid cancers will not grow or change because they appear indolent or dormant. However, about 5% to 10% will increase in size (typically by several millimeters) and notably 1% to 2% will develop new local lymph node metastases. A notable finding from the previously mentioned work was that younger patients were more likely to harbor mPTCs that grew or locally spread (6). This argues for greater consideration of surgical intervention in young patients. Brito and colleagues have published a framework to help guide risk assessment and clinical decisions in such settings (7).

Separate data, however, also help guide an approach to nonoperative intervention. Notably, Wang and colleagues demonstrated that older patients (age > 70 years) are at greater risk of other serious comorbid illnesses in addition to that posed by small or low-risk thyroid carcinoma (8). Over a mean of 4 years, nearly 14% of patients older than 70 years presenting for nodule evaluation died of other nonthyroidal comorbid diseases, whereas only approximately 1.5% of cases proved to be significant-risk thyroid cancer. All of these significant risk cancers were identifiable at time of initial assessment with use of just ultrasound and fine-needle aspiration.

Thus, a reasonable conclusion is that most patients older than 50 years with significant comorbid illness, and perhaps any patient older than 70 years, with a biopsy-proven mPTC (and a low-risk sonographic profile), should be a candidate for nonsurgical active monitoring of such lesions when identified. Similar consideration could be considered for even younger patients, especially as the size of any identified mPTC is smaller (eg, < 5 mm). Perhaps the most important recommendation is to temper the need for diagnostic testing (UG–fine-needle aspiration) when any sonographically low- or very low-risk nodule smaller than 1.5 cm is identified, outside unique circumstances. This is critical because patient decision making following a biopsy-proven malignancy (even if just 3-5 mm in size) can drive care decisions far afield from data-driven paradigms, given anxiety. Critical to the future will be the design and execution of large, well-designed, prospective, and randomized trials in this area, allowing high-quality evidence to then set metrics and force practice patterns worldwide.

But for patients with biopsy-proven mPTC for whom intervention is currently being considered following thoughtful and careful assessment, a minimally invasive strategy using MWA or ethanol ablation should be strongly considered. The simplicity, safety, cost, and effectiveness of this approach suggest it is superior to surgical intervention.

Abbreviations

Abbreviations
 
• mPTC

  micropapillary thyroid carcinoma

 
• UG-MWA

  ultrasound-guided microwave ablation

Additional Information

Disclosure Summary: The author has nothing to declare.

Data Availability: Data sharing is not applicable to this article as no datasets were generated or analyzed during the current study.

References