Recurrence rates and the need for follow-up

1. Introduction
2. Recurrence rates and the need for follow-up
3. Thyrogen in follow-up
4. Summary
5. About the Author

Although the long-term prognosis for survival with WDTC is generally quite good, tumor recurrence is common, affecting about 6% of all patients at 5 years and about 10% at 10 years after initial therapy; however, the rate increases with tumor size, being about 4% with small tumors < 1.0 cm and 25% with tumors > 8 cm.(4) Recurrence can occur any time, even decades after initial therapy.^[1,2] Studies now show that many late cancer "recurrences" may actually be cases of persistent tumor that had fallen below our testing detection limits for as long as decades.^[2]

In one recent study, persistent was found in nearly 20% of 107 differentiated thyroid carcinoma patients over a three- to five-year period. Tumor was found in 81% of treated patients with an initial or follow-up recombinant human (rh)TSH-Tg greater than 2 ng/ml.^[3]

Given the potential for this type of "recurrence" due to persistent tumor, and knowing the percentage of thyroid cancer deaths caused by WDTC, there is believed to be risk associated with delay of detection of small amounts of recurrent tumor. We know that delaying the initial diagnosis of thyroid cancer longer than 1 year increases mortality rates significantly. The mortality risk worsens as the delay becomes longer, eventually imparting a risk comparable with that of advanced age. One study, based on regression modeling of 1510 patients without distant metastases at the time of initial therapy who had undergone surgery and I-131 therapy, found that the likelihood of death from WDTC was increased by multiple factors.^[1] These included age of over 40 years, a tumor size of more than 1.0 cm, local tumor invasion or regional lymph node metastases, follicular histology, and a delay of therapy for more than 12 months and the extent of surgery and use of I-131 therapy.^[1]

There are compelling reasons to believe that delay-related risks also exist with persistent, unrecognized thyroid cancers. For example, respiratory insufficiency due to pulmonary metastases is the most common cause of thyroid cancer death. Additionally, tumor bulk of distant metastases ranks second only to patient age as a predictor of death from thyroid cancer. The longer the tumor remains, the greater its bulk. However, early diagnosis and treatment substantially enhance survival.

In addition to the risk of increasing tumor bulk as a result of delay in disease identification and treatment, there is also evidence indicating that if left untreated, the tumor can transform into dedifferentiated forms of thyroid cancer, including anaplastic thyroid cancer. Many anaplastic thyroid cancer cases arise in patients with a history of thyroid disease, including goiter or treated well-differentiated thyroid cancer. Dedifferentiated thyroid cancer is typically much more aggressive and difficult to treat than well-differentiated forms of the disease.^[4]

These facts lead us to two important possible conclusions: 1) that delay of diagnosis and treatment can be directly related to a higher mortality rate, and, conversely, 2) that early identification and treatment of recurrent and/or persistent WDTC can lower mortality rates. Meticulous initial therapy coupled with rigorous follow-up can have very favorable effects on patients with WDTC.

1. Introduction
2. Recurrence rates and the need for follow-up
3. Thyrogen in follow-up
4. Summary
5. About the Author

REFERENCES:

1. Ries, LAG, Eisner MP, Kosary CL, et al. 2000 SEER cancer statistics review, 1973-1997. Bethesda, MD: National Cancer Institute.

2. Hundahl, SA, Fleming ID, Fremgen, AM, Mench, HR. 1998 A National Cancer Data Base Report on 53,856 cases of thyroid carcinoma treated in the US, 1985-1995. Cancer. 83:2638-2648.

3. Kloos RT, Mazzaferri EL. A single recombinant human thyrotropin-stimulated serum thyroglublin measurement predicts differentiated thyroid carcinoma metastases three to five years later. J Clin Endocrinol Metab 2005; 90:5047-5057.

4. Hunt et al, Am J Pathol, Vol 27, No 12, December 2003