Sunday, May 4, 2014

Hints for Screening Tests in Familial Thyroid Cancer

There is a rare form of thyroid cancer known as medullary thyroid carcinoma (MTC), which can be familial; meaning that it is a germ line cancer.  MTC only accounts to about 3-10% of all thyroid cancers but is responsible for about 13% of all deaths from a thyroid cancer. This study looked at hereditary MTC as well as multiple endocrine neoplasia 2 MEN 2 (A and B), sub-classifications of MTC.  MEN is a medical disorder where tumors grow in endocrine organs and cause problems originating in the thyroid.  Type 2A is a condition in which excess parathyroid hormone is secreted and type 2B can cause neurofibromatosis.  The findings from this paper suggest that inherited MTC is detected earlier in life and treated, where as sporadic MTC is not detectable and results in more deaths..

Table 1 Clinical Characteristics of Patients with Sporadic and Hereditary MTC.  Mean ages, symptoms and staging of the various sub classifications of MTC.
 The data above suggests that there are more sporadic occurrences of MTC(more than half) verses all of the other sub-classifications, 79% of the patients having sporadic thyroid cancer.   But the sporadic MTC was not prevalent in a patient until about the age of 47, where other cases were detected at a mean age of 24 (sporadic mean age 49% greater than that of the others combined.)  This delay in diagnosis explains why so many of the sporadic cases were in stages III or IV, where the other cases were mostly in stages I.  By not detecting the cancer earlier in the patients life the cancer was allowed to grow and spread increasing the lethality.  Later stage cancers are harder to cure and therefore more people can die from this late diagnosis. 
Tumors are one of the hallmarks of cancer and become one of the first visible symptoms of cancer.  In this study there are very few cases of tumors in MEN2A and familial MTC, but more than half of them had a family history of their disease (56%).  But very few of those with MEN2A and familial MTC had stage III and IV cancers, which means they are more susceptible to screening. Having a familial history of the disease is an indicator of MTC and seems to call for an early screening. Whereas the sporadic cases seem not as prone to screening considering that 60% of the sporadic cases were stage III or IV.  The high incidents of late staging could be because of the fact that a patient does not show symptoms of thyroid cancer until a nodule has accumulated.  At which point the cancer has progressed to stage III or IV.  The earlier screening allows for early treatment to prevent the staging of cancer to progress.
Figure 1 Cancer specific cumulative survival by Kaplan–Meier analysis is shown for all patients with medullary thyroid carcinoma. (A) Survival for patients ages < 45 and ≥ 45 years is compared with (B) survival by TNM stage of disease at presentation.
In part A of figure 1 above we see that most patients survive for at least 20 years, and those patients older than 45 only living that long after.  The younger the patient was at diagnosis the better chances they had at surviving.  In order to be diagnosed with MTC at such a young age would mean that the patient needs a family history of MTC. Without that history patients did not show symptoms until later in life, closer to 45, by which time their cancer had progressed into later stages. In part B we see that stage IV cancers have a lower mean survival than any of the other stages.  The lower survival rate is due simply to the fact that stage IV cancers are harder to cure.  So, what does this all mean?
This data suggests that a family history of cancer is an indicator for thyroid cancer, and that early screening leads to an early diagnosis that allows for a better treatment and longer survival.  But those without a family history of thyroid cancer seem to not to show symptoms of a cancer until there is a tumor growth, at which point the data suggests that the tumor has progressed further and there is a higher chance of death.
To prevent the cases of this cancer from going any higher a better screening test should be established.  A test that is able to detect the sign of thyroid cancer sooner in life rather than later.  An earlier detection of the cancer would give the patient a better chance at survival.  We should study those with familial MTC to try and understand the early signs of thyroid cancer or the genetic makeup of the cancer as to design the test to detect early onset thyroid cancer.

"Medullary Thyroid Carcinoma." Wiley Online Library. Cancer, 1 Mar. 2000. Web. 4 May 2014.