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BACKGROUND

  1. Top of page
  2. BACKGROUND
  3. LITERATURE REVIEW
  4. BEST PRACTICE SUMMARY
  5. LEVEL OF EVIDENCE
  6. BIBLIOGRAPHY

There has been substantial recent debate over the best surgical treatment for papillary thyroid microcarcinoma (PTMC), defined as a carcinoma less than 1 cm in size. As the incidence of patients with these subcentimeter tumors increases, the question of whether to peform a total versus a hemithyroidectomy for these lesions has become increasingly important. Historically, treatment of any thyroid malignancy entailed total thyroidectomy both for eliminating tumor surgically and for clearing normal thyroid tissue prior to postoperative radioactive iodine ablation. This paradigm has slowly shifted with recent guidelines put forth by the American Thyroid Association in 2009 espousing conservative management of PTMC with hemithyroidectomy alone. However, as demonstrated by a recent survey study by these authors, clinical practice in the surgical community is more mixed with a significant minority of surgeons (30%) believing total thyroidectomy to be the appropriate treatment.1

LITERATURE REVIEW

  1. Top of page
  2. BACKGROUND
  3. LITERATURE REVIEW
  4. BEST PRACTICE SUMMARY
  5. LEVEL OF EVIDENCE
  6. BIBLIOGRAPHY

Several studies have examined the effect of extent of thyroidectomy in patients with PTMC. Many early studies recommended total thyroidectomy, with more recent studies tending to be more conservative. A study from Hay et al.2 at the Mayo clinic in 1992 reported on a series of 535 patients with PTMC treated over a 50-year period, demonstrating a higher recurrence rate in patients who had nodal metastases and in those who underwent hemithyroidectomy. Given the large numbers of this review, the recommendation for total thyroidectomy was highly influential. Multiple studies both in the United States and abroad concurred with these initial findings.

Particularly, much of the international literature endorses an aggressive treatment paradigm, consisting of total thyroidectomy, for unifocal PTMC. A large retrospective chart review of 203 patients from Chow et al.,3 in 2003, demonstrated a 25% prevalence of lymph node metastases, 2% distant metastases, and 1% mortality rate in their patient population. Although their study demonstrated no overall survival advantage comparing total to hemithyroidectomy, they cited a reduction in locoregional recurrence in those patients without initial positive lymph nodes who underwent total thyroidectomy and radioactive iodine therapy (from 7%–0%). Despite an overall excellent overall prognosis, the authors recommended total thyroidectomy with consideration for central node dissection and postoperative radioactive iodine depending on individual patient factors. Mirroring this sentiment, in 2002, the British Thyroid Association and the Royal College of Physicians released guidelines recommending total thyroidectomy and routine radioactive remnant ablation in cases of PTMC, which at that time differed significantly from the current American guidelines.

Table I. Summary of PTMC Literature
AuthorsSizeFindings and Recommendations
Chow et al., 20033<1 cmFindings: 25% lymph node metastases, 2% distant metastases, and 1% mortality rate. Gave RAI to pataients with extrathyroidal extension, local and distant metastases, age over 40, or gross residual disease. No survival benefit comparing total versus hemithyroidectomy but found nonsignificant decrease in locoregional recurrence with total thyroidectomy and RAI.
Recommendation: total thyroidectomy with or without RAI depending on presence of poor prognostic factors
Hay et al., 20084<1 cmFindings: 900 consecutive cases at Mayo Clinic. Comparing hemithyroidectomy versus total thyroidectomy, they found no significant difference in locoregional recurrence rate at 10, 15, and 20 years: 5.7%, 5.7%, 9.8% versus 4.5%, 4.7%, 5.5%. Postoperative RAI also did not improve locoregional or lymph node recurrence rates.
Recommendation: hemithyroidectomy for low-risk PTMC
Ito et al., 20035<1 cmFindings: recommended surgery for patients with high-grade lesions by FNA, lymph node metastases, and tumors adjacent to trachea or recurrent laryngeal nerve. Offered observation versus surgery for nonhigh-risk lesions. In 162 patients that chose observation, 70% did not increase in size over 5 years; 11% grew to > 1 cm; 11% had suspicious lymph nodes in central compartment that did not grow, and only 1% had lymph node spread to lateral compartment.
Recommendation: low-risk PTMC may be observed or managed conservatively
Table II. Comparing the Current American and British Thyroid Association Reccomendations
American Thyroid Association 2009“Lobectomy alone may be sufficient treatment for small (<1 cm), low-risk, unifocal, intrathyroidal papillary carcinomas in the absence of prior head and neck irradiation or radiologically or clinically involved cervical nodal metastases.” Low risk: no lymphovascular invasion, evidence of more aggressive cellular variants, and age <45 years old
British Thyroid Association 2007“Patients with-low risk PTC ≤1 cm diameter may be treated with thyroid lobectomy alone.” Low risk: age <45 years old, no distant metastases

Recently, the majority of studies have described PTMC as a low-grade malignancy that can be treated with hemithyroidectomy alone. In a follow-up study in 2008, Hay et al.4 reviewed 900 cases of PTMC over a 60-year period and found that overall these patients have an excellent prognosis and found no difference in recurrence rates between those patients who underwent unilateral lobectomy and those treated with total thyroidectomy, contradicting the findings of his earlier study.

A very persuasive example of the more benign nature of this disease was demonstrated in a study by Ito et al.,5 who followed 162 patients with PTMC with observation alone for up to 6 years. He found the majority (70%) of tumors had no change in size or actually regressed. Only 1% developed lymph node metastases, and 10% grew to greater than 1 cm. Given these data, they suggested that serial imaging and physical examination may be possible in properly informed patients. Table I summarizes some of the recent literature pertaining to treatment of papillary thyroid microcarcinoma.

However, although many authors support conservative management of PTMC, there are certain patients for whom aggressive treatment may be needed. Capsular invasion, extrathyroidal extension, and lymph node metastases have been found to be signficant factors for both locoregional and distant recurrence. In addition, more aggressive forms of papillary thyroid carcinoma, including tall cell variants, associated laryngeal paralysis, prior radiation, and other comorbidities, may have higher locoregional recurrence, distant metastases, and overall mortality. Atlhough age and gender are prognostic indicators in papillary thyroid carcinoma greater than 1 cm, there have been no studies to date demonstrating age or gender-related increased recurrence or mortality in PTMC.

BEST PRACTICE SUMMARY

  1. Top of page
  2. BACKGROUND
  3. LITERATURE REVIEW
  4. BEST PRACTICE SUMMARY
  5. LEVEL OF EVIDENCE
  6. BIBLIOGRAPHY

Despite conflicting conclusions from different authors regarding the optimal treatment for PTMC, overall survival of this disease is excellent regardless of the extent of initial treatment. The majority of studies point toward hemithyroidectomy as adequate treatment for PTMC without sacrificing future locoregional control. Close clinical follow-up and proper informed consent are critical for these patients, with physical examination and serial imaging done at regular intervals. Prognostic indicators that may lead to more aggressive treatment of PTMC include extracapsular invasion, lymph node metastases, previous radiotherapy, age, and aggressive histologic variants. Long-term outcome studies are needed, with at least 20-year follow-up data, in order to fully assess the prognostic significance of these factors in PTMC.

The British Thyroid Association and the American Thyroid Association released revised guidelines in 2007 and 2009, respectively, and are now in agreement with each other in their recommendation for thyroid lobectomy for PTMC (Table II).

LEVEL OF EVIDENCE

  1. Top of page
  2. BACKGROUND
  3. LITERATURE REVIEW
  4. BEST PRACTICE SUMMARY
  5. LEVEL OF EVIDENCE
  6. BIBLIOGRAPHY

No prospective randomized controlled trial comparing the effect of lobectomy versus total thyroidectomy on survival and locoregional recurrence exists. Because the prognosis for these patients is so favorable, such a study would have to accrue an exceptionally large patient cohort to demonstrate significant differences and would not be a pragmatic endeavor. The studies reviewed here are all large retrospective chart reviews or database analyses and are therefore level II evidence.

BIBLIOGRAPHY

  1. Top of page
  2. BACKGROUND
  3. LITERATURE REVIEW
  4. BEST PRACTICE SUMMARY
  5. LEVEL OF EVIDENCE
  6. BIBLIOGRAPHY