Thyroid Cancer: 20-Year Comparative Mortality and Survival Analysis of Six Thyroid Cancer Histologic Subtypes by Age, Sex, Race, Stage, Cohort Entry Time-Period and Disease Duration (SEER*Stat 8.3.2) A Systematic Review of 145,457 Cases for Diagnosis Years 1993–2013
Background.—Incidence and prognosis of cancers of the endocrine glands vary greatly by stage and histologic type, and, thyroid cancer accounts for most (92%) of the cancers of the endocrine glands. It is the 8th most common of cancers and has been rising in incidence since 1975. It remains a formidable health threat in the United States in 2016 with estimated cases of 64,300 and 1980 deaths.
Objective.—Provide 20-year comparative mortality analysis of thyroid cancer in a recent group of 145,457 staged cases (97.5%) of a total of 149,202 patients during the 1993-2013 entry time-period in six histologic subtypes by age, sex, race, stage and disease duration.
Methods.—Population-based data from SEER registries,1 1973-2013, (SEER*Stat 8.3.2.) were analyzed.
Results.—Tables 1-8 provide basic SEER epidemiologic, demographic, case-statistics, and comparative mortality follow-up data of 4 principal and 2 supplementary thyroid cancer oncotypes by age, sex, race, stage and disease duration of patients in the 1993-2013 time-period.
Conclusions.—Thyroid cancer when localized has a very good prognosis, with no significant excess mortality after diagnosis in papillary and papillary follicular variant cancers (PFV). Because nearly two thirds of thyroid cancers are localized, and excess death rate (EDR) is small in patients with regional cancer under age 50, overall excess mortality for all ages also virtually disappeared after 10 years in papillary and follicular cancer. Overall, the 5-year survival rate is greater than 90% for papillary and follicular carcinomas. Nevertheless, because of the marked predominance of papillary carcinoma, the continued increase in its relative frequency and annual projected deaths, thyroid carcinoma remains a significant health concern in the current era.
Introduction
From 1974-2013, the overall incidence of thyroid cancer has increased 3% annually. The incidence and mortality rates for advanced stage papillary thyroid cancer has also expanded. These findings are consistent with a true increase in the occurrence of thyroid cancer in the United States.2 According to the National Cancer Institute (NCI)-Thyroid Cancer Treatment (PDQ) – Health Professional Version (December 15, 2016), there are 4 main histologic types of thyroid cancer: papillary, follicular, medullary & anaplastic. However, according to the International Classification of Diseases for Oncology, Third Edition, topography code C739 for thyroid cancer in the SEER Site/Validation List (September 18, 2015), nearly 60 oncologic histology variants for the thyroid gland are enumerated. Also, the thyroid gland may occasionally be the site of other primary tumors, including sarcomas, lymphomas, epidermoid carcinomas, and teratomas. Moreover, the thyroid may also be the site of metastasis from other cancers, particularly of the lung, breast, and kidney.
Methods
Data Sources
Population-based data from SEER Registries Research Data, 1973-2013, were analyzed.
Life Table Methodology
The application of life table methodology to risk appraisal has been well described by Singer,3,4 Pokorski5 and others.6
Thyroid Site Code (TSC)
The site code is taken from the coding system utilized for all diseases in A Descriptive Index of Mortality Studies from Selected Sources, 1991-1995.7 In this Index, the 3-digit code for thyroid cancer is 174; the first digit indicates malignant tumor and is omitted for this cancer publication, hence the index site code – IC74, for thyroid cancer.
Demographics Characteristics
This analysis included sex, race, age and mean age at diagnosis.
Case Characteristics
Thyroid cancer cases (International Classification of Diseases for Oncology, Third Edition; topography code C739) were classified according to histologic type. Four principle histologic oncotypes and 2 other commonly considered subtypes were selected for mortality analysis including: 1) Papillary adenocarcinoma, NOS (8260), 2) Follicular adenocarcinoma, NOS (8330), 3) Medullary carcinoma, NOS (8510), 4) Undifferentiated and anaplastic carcinoma (8020-8021), 5) Oxyphilic adenocarcinoma-Hurthle cell (8290), and 6) Papillary carcinoma, follicular variant-PFV (8340).
Incidence-Based Mortality Rates (IBM)
The 6 thyroid cancer histologic subtypes in this report (see Table 2) were selected for long-term comparative mortality analysis after determining case statistics by performing frequency & mean age (FAMA) queries, and distribution analysis by age, sex, race and stage from the SEER database to aid in the selection of age-related durational-interval groupings for mortality analysis, and to ascertain distribution data by age, sex, race, tumor stage, cohort-entry period and other case-statistic properties. Therefore, unlike traditional mortality rates, IBM rates for this report were examined according to site selection variables recorded at diagnosis (eg, histology, stage, grade, etc) and available in the SEER*Stat program.
Cancer Stage
The SEER Stage LRD “Historic Stage Recode A” was used to classify thyroid cancer cases by stage as localized (confined within the thyroid capsule), regional (tumor extension beyond the limits of the thyroid gland or spread by more than 1 lymphatic or vascular supply route to tissues adjacent to the thyroid gland or to regional lymph nodes), or distant (further direct extension or extracervical metastasis to other organs) in order to utilize cases coded and entered as far back as 1973. Parenthetically, many revisions have been made in SEER coding since 1973, but cases so coded have survival data only from the year in which the new code was put into use. For instance, the Stage I-IV, or, TNM codes of the American Joint Committee on Cancer (AJCC) were not used by SEER until 1988 and have undergone further revisions in 2004 and again in 2010.
Histologic Grade
Grading of malignancy is excluded because only a small proportion of cases were graded (21.5% since 1973). Only microscopically confirmed cases are included. Thyroid cancer cases were excluded if the diagnosis was made in a death certificate or by autopsy, if the case was unstaged, and if there was a previous or current additional cancer. Patients have been subdivided by age, sex, stage and histological type into the combinations that appeared to be most informative in a limit of six pages of mortality tables (Tables 3-8) and 2 tables illustrating descriptive epidemiologic and demographic case statistics (Tables 1 & 2).
Statistical Significance
Standard errors are shown for the survival rates in the SEER survival tables. In the SEER program, the actuarial method: Ederer II method is used for cumulative expected survival. Ederer II method calculates the expected survival rates for patients under observation at each point of follow-up. So, the matched individuals are considered to be at risk until the corresponding cancer patient dies or is censored. Also, confidence interval: Log (-Log ()) Transformation; the level is 95% is adhered to. Poisson confidence intervals at the 95% level based on the number of observed deaths in this study are not displayed here to conserve space on mortality tables.
Results
Incidence & Mortality Rates
According to the SEER Cancer Statistics Review 1975-2012,8 age-adjusted incidence rates in 2008-2012 were 20.0 per 100,000 in women, but only 6.2 per 100,000 in men. Annual delay-adjusted SEER incidence rates increased from 4.85 per 100,000 in 1975 to 15.24 per 100,00 in 2012. In 2012, delay-adjusted incidence was 22.15 per 100,000 in females and 8.20 per 100,000 in males (CSR Table 26.4). Age variation in overall incidence is smaller than in most cancers. In the 2008-12 time-period, the rate per 100,000 is just 8.9 in persons 10-24 years, 9.8 in young adults 25-29, increasing gradually to 24.4 at ages 60-64, then decreasing to 11.3 at ages 85 and up. By race the lowest rate was in blacks (8.0), and the highest in white non-Hispanics (15.1). The trend in overall SEER incidence was upward from 2008-12, with an Average Annual Percent Change (AAPC) of +2.8%. Age adjusted US mortality rates, 2008-12: All ages 0.5 deaths per 100,000, under 65 (0.1), 65 and over (3.0).
Case Statistics & Main Epidemiologic Characteristics
The epidemiology and case distribution characteristics of the 1993-2013 study population is shown in Tables 1 & 2. Table 1 is an overview summary of incidence rates and trends by age & mean age at diagnosis, sex, race, stage distribution and 5-year survival rates in a total of 149,202 cases of invasive thyroid carcinoma in the SEER frequency database, all histologic subsites combined. Table 2, Figures 1-6 illustrates the statistical distributions of frequency & mean age, sex, race and stage for each thyroid cancer oncotype studied. Both similar and different demographic, epidemiologic and biostatistical trends and patterns reflect differing biologic entities except for the PFV variant. The total of 149,202 cases is higher than the total of 130,028 in the survival database due to the routine exclusion of cases lacking follow-up (FU) or due to lack of staging. Incidence by quinquennial age from birth is displayed in graphic form and indicates that thyroid cancer in males & females begins early in life. Incidence in females reaches its zenith at 45-49 years, then smoothly declines to age 85+ years. Male incidence reaches a plateau at 50-59 years and then gradually diminishes to age 85+ years.
Of patients with thyroid cancer, 51.2% are under 50 years of age. Younger patients under 35 constitute 18.5% of the total, subdivided into 13.4% by age 25-34, 4.7% age 15 to 24, and about 0.5% in children under age 15. Females (113,110; 75.8%) outnumbered males (36,092; 24.2%) by more than 3 to 1. Whites (121,960; 81.7%) outnumbered blacks (9,691; 7.9%) by a wide margin. Mean ages in males 53.24 years, females 48.34, whites 49.62, blacks 50.5, other including American Indian/Alaska Native, Asian/Pacific Islander 44.84, and unknown 44.36. A very small number of in-situ cases were from the total.
By stage, almost two thirds of the cases were localized, one third regional, 4.5% distant, and 2.5% unstaged. These characteristics differ sharply from those of the typical major cancer site, with few patients under 45, a more even sex distribution, and a minority of patients in the localized stage. Median survival was more than 20-years, 5-year relative cumulative survival (100P/P’) was 97.6% and 5-year observed cumulative survival (P) was 93.7%.
Mortality Analysis by Histologic Oncotype
Prior to accomplishing long-term thyroid cancer comparative mortality analysis on 6 histologic subsets, 130,028 cases of invasive thyroid cancer (all histologic subtypes, age, sex and race combined in the SEER*Stat 8.3.2 survival database utilizing the cohort entry-period 1993-2013) were first examined to obtain an overview understanding of the nature and magnitude of the risk, the mathematical burden of excess mortality, and projected observed, expected and relative cumulative survival. Aggregate average annual mortality and survival results (all sites combined) are displayed below for the following durational intervals: 0-1, 1-2, 2-5, 5-10, 10-15 and 15-20 years. (See Chart 1).
Observed (actual) deaths exceeded expected deaths by more than 3 to 1 in the first duration and is reflected in a mortality ratio (MR) of 332% and excess death rate (EDR) of 17.9 per 1000. Observed deaths are higher than expected deaths in virtually all durational intervals and mortality ratios are high for the first 5 years of follow-up, but then drop to almost normal levels. Five-year observed cumulative survival (P) is >90% but drops to 77% in 20 years. However, relative cumulative survival (100P/P’) remains above 95% in all durations. Interval expected cumulative survival (P’) is displayed.
Papillary Carcinoma (ICD-O-3, 8260)
Papillary carcinoma is the most common type of invasive thyroid cancer, accounting for 42.4% of total cases in the SEER*Stat frequency database for the 1993-2013 cohort entry-period period. Table 2-Figure 1 case statistics indicate that this histologic tumor accounted for 76.0% in females, 81.1% in whites but only 5.0% in blacks. Of patients with papillary thyroid cancer, 56.3% have localized disease at the time of diagnosis, 38.0% have regional involvement, 3.6% have distant metastasis, and 2.1% are unstaged. Mean age at diagnosis for whites and blacks was 48.47 and 49.45 years, respectively. Mean age was higher by more than 4.5 years in males vs females, 51.59 and 47.04, respectively.
Prognosis of papillary carcinoma is excellent. Comparative mortality for localized papillary carcinoma is shown in Tables 3 & 7. There is no excess mortality by sex or race for local stage disease and the relative cumulative survival ratio is 100% or above in both sexes and by race. Mortality at 20 years is not statistically significant due to minimal exposures and deaths. Excess mortality for regional disease continued to be modest in white males at 5 and 10 years with mortality ratios of 145 & 135, respectively, and respective EDRs of 4.7 and 4.2 deaths per 1000. For both durations, relative cumulative survival ratios were above 95%. Excess mortality in white females for regional disease was modest with mortality ratios at 5 and 10 years of 132 & 107 with respective EDRs of 1.8 and 0.5 per 1000. Relative survival at these intervals remained at 99% or above. In black males, excess mortality in regional disease was quite high with a mortality ratio of 353 and EDR of 32.1 per 1000 in the first duration but at 5 and 10 years dropped to an MR of 159 & 98 and EDR of 7.0 & -0.3 per 1000 respectively. Excess mortality for regional disease in black females was similar to that in black males with an initial high MR and EDR in the first interval of 330 & 16.8 per 1000 but dropping to an MR of 136 and EDR of 2.7 per 1000 by 5 years. Relative survival remained above 95% at 10 years.
Only 2254 cases of papillary carcinoma with distant extension or metastasis were contained in the 1993-2013 SEER database, 3.6% of the total of 63,198 cases of invasive cancer in this site. In the source database queries (not displayed here), excess mortality was very high by sex and race, decreased progressively with duration, but was still present in both sexes and all races at duration 15-20 years. For instance, the initial 0-1-year duration MR and EDR for distant disease in white females was 1026 & 106.5 per 1000, respectively, but progressively diminished to 174 and 5.2 per 1000 at duration 15-20 years. At the 15-20-year duration, observed survival was 62.4%, and relative survival ratio was 71.9%. Expected cumulative survival was 86.7%.
Follicular Carcinoma (ICD-O-3, 8330)
Follicular carcinoma (ICD-O-3, 8330) (papillary carcinoma-follicular variant aside) is the second most common type of invasive thyroid cancer, accounting for 4.4% of total cases in the SEER*Stat frequency database for the 1993-2013 cohort entry-period. Table 2-Figure 2 case statistics indicate that this histologic tumor accounted for 77.1% of follicular cancers in whites but only 12.1% in blacks. Similar to papillary carcinoma, almost two and a half-fold excess female preponderance, is observed for follicular carcinoma. At all ages, incidence rates are higher for females than for males in both whites and blacks. Mean age at diagnosis was similar for whites and blacks, 51.97 vs. 51.75, respectively, but higher by 6 years in males than females.
Of patients with follicular thyroid cancer, 51% have localized cancer at the time of diagnosis, 37% have regional involvement, and 8.6% have distant metastasis while 3.3% were unstaged. Table 7 and 8 indicate that similar to papillary cancer, men are proportionally more likely than women to be diagnosed with nonlocalized disease. Excess in advanced stages is also found in blacks, contrasting with the pattern of papillary cancer. The proportion of black patients with follicular thyroid cancer spread to distant organs is less than that of whites (3.53% vs 4.96%) perhaps indicating more expeditious diagnosis and treatment in blacks in recent years.
In localized follicular cancer, all ages combined (Table 4), the notable finding is that excess mortality is seen only in the first year of follow-up with a mortality ratio (MR) of 157% and EDR of 4.9 per 1000, both sexes combined. There was no significant excess mortality in any of the 5 duration intervals from 1 to 20 years, the MR ranging between 87% and 111%, all ages combined. Observed (actual) mortality rates, q, were consistently lower than the matched population rates, q’, at durations 1-2 and 2-5 years. In the last three 5-year duration intervals, there were only minor, apparently random variations from an MR of 100%.
Excess mortality in regional follicular thyroid cancer continued to be minimal in patients under 50 years, male and female combined. The MR ranged between 171% & 173%, and the EDR from 1.1 to 1.2 per 1000 per year (Table 4). However, EDR rose sharply with age in the first year, from 1.1 in those under 50 to 22.3 in those over 50. When all ages were combined, the pattern of progressive decrease of EDR from 0-1 year to 10-15 years is notable. The EDR decrease to -6.4 at the 15-20 duration is based on a small exposure with 11 deaths (95% CL 5.5 to 19.7), a change that is not statistically significant.
The total 1973-2013 SEER survival database was used to garner sufficient cases by age, sex, race and stage for detailed mortality analysis. Five and 10-year comparative mortality and cumulative survival indices by sex and race, all stages combined noted in Tables 7 & 8 for follicular carcinoma are shown in Chart 2.
In Table 7, mortality ratios and excess death rates are similar in white males and females at 0-5 & 5-10 year durations and cumulative survival ratios are 90% or above. The 5-year relative survival rate in white males of 41.6% for distant follicular carcinoma is only about half that for distant papillary carcinoma (72.9%), suggesting a different natural history in these histologic types. The prognosis for white males, and females is similar when compared within stage. In black males and females at the 0-5-year duration, EDRs were much higher and observed and relative survival lower than in their white male and female counterparts.
Medullary Carcinoma (ICD-O-3, 8510)
Medullary carcinoma of the thyroid is uncommon. It is so named because a specialized cell in the thyroid gland, the perifollicular calcitonin-producing C cell, which regulates calcium metabolism may become malignant. Tumors from these cells are called “medullary” carcinomas. It accounts for only 2156 (1.4%) of all invasive thyroid cancer cases in the 1993-2013 SEER frequency database, and 1827 total cases in the SEER survival database. The proportions tend to be higher in women (58.1%), than in men (41.9%). A preponderance in medullary carcinoma in the SEER frequency database is observed for whites, 1829 – 84.8%, but not for blacks, 173 – 8.0% (Table 2, Figure 3). This compares with the patterns of papillary and follicular carcinomas; papillary – whites >81.1% higher than blacks, and follicular – whites >77.1% higher than blacks. The mean age at diagnosis is lower in females than in males, 52.7 years vs 54.84 years. The mean age in whites is much higher than the mean age in blacks, 54.18 vs 51.18. Rates in females begin to rise at ages 15-19, 10 years earlier than in males at ages 25-29, and reach a higher peak at age 50-54. During the entire 1993-2013 period, only 145 cases all stages combined and a total of 31 deaths in blacks are reported in the SEER survival database (black survival & mortality tables not displayed). The small number precludes detailed analysis by race.
About half the cases are localized at diagnosis, 33.5% have regional involvement, and 13.9% show distant metastasis (Table 2, Figure 3). For localized disease (Table 8), mortality and survival at 5-years are: MR 92%, EDR -0.9 per 1000, and cumulative observed survival and relative survival 94.9% and 100.7%, respectively). For regional disease, mortality and survival are less favorable with median observed and relative survival just slightly more than 14 years. At the 0-5 and 5-10 year durations, MR is 345% and 280%, and EDR is 25.7 & 20.6 per 1000, respectively. In these durations, cumulative survival ratios decline to 87.8% and 77.9%, respectively. Prognosis worsens with distant metastasis. At 5-years, the MR and EDR are 1314% and 158.7 per 1000, respectively. At 10-years, the relative survival falls to 27.2% (Table 8). When all stages are combined, mortality ratios do not decline below 250% until after 10 years.
Undifferentiated & Anaplastic Carcinoma (ICD-O-3, 8020-8021)
Table 2-Figure 4 case statistics indicate that anaplastic, or undifferentiated carcinoma, is a very rare histologic type of thyroid cancer, accounting for approximately1349 (0.9%) of total cases in the SEER frequency database in the 1993-2013 time-period. Tumors of follicular cell origin may fail to differentiate, in which case they give rise to the “anaplastic” or “undifferentiated” carcinomas. Table 2-Figure 4 case statistics also indicate that this histologic type of tumor rises substantially only after the sixth decade of life. After age 50, age-specific incidence curves in females continues to increase with age reaching a high point at 85+ years, whereas in males it reaches a plateau at age 65 and then begins a slow steady decline. Mean age at advanced diagnostic ages is less in males than in females, 67.7 & 72.6, respectively. For all races, mean ages are: whites 70.6, blacks 68.6, other 70.4, and unknown 70.3. In general, the anaplastic carcinomas are advanced at the time of diagnosis.
Only 1239 cases were available in the SEER survival database from 1973-2013 for a comparative mortality analysis (Table 6). Prognosis for anaplastic carcinoma is extremely poor. Initial excess mortality is extremely high, but decreases progressively with duration. MR and EDR at the 0-1 duration are 2282 and 781 per 1000. MR and EDR at the 1-2 year follow-up duration are 1428 and 332 per 1000. At the 5-year follow-up duration, MR, EDR and relative cumulative survival are 520%, 101.8 per 1000, and 9.1%, respectively, contrasting with the superior comparative mortality and survival indices for papillary, follicular and medullary carcinomas (Table 6). Mortality is not statistically significant after 5-years due to minimal exposures and deaths.
Oxyphilic Adenocarcinoma – Hurthle cell (ICD-O-3, 8290)
Oncocytic or oxyphilic carcinomas (also called Hurthle cell carcinoma) is a relatively rare variant of follicular carcinoma and behave as a slightly more aggressive form of follicular cancer but present similarly. It is an uncommon invasive thyroid cancer, accounting for 4006 (2.7%) of total cases in the 1993-2013 SEER frequency database. There were 3307 cases in the SEER survival database in the 1993-2013 time-period and a moderate female preponderance (2797 cases – 69.8%). Male and female mean ages are 59.9 and 56.5 years, respectively. Mean age in whites and blacks are 57.7 and 56.1, respectively. Female incidence reaches its zenith at 50-54 years, plateaus and then sharply declines at 70-74 years. Male incidence reaches its zenith 5 years later, plateaus and then begins a slower decline at 70-74 years. 53.1% are local stage at diagnosis, 40.6% are regional stage, 3.9% are distant and 2.2% are unstaged. Aggregate average annual mortality and survival results, 1993-2013, are displayed below for the following durational intervals: 0-1, 1-2, 2-5, 5-10, 10-15 and 15-20 years, all ages, races and stages combined (See Chart 3).
Observed (actual) deaths exceeded expected deaths by 2 to 1 in the first interval and is reflected in a mortality ratio (MR) of 188% and excess death rate (EDR) of 12.9 per 1000. Mortality in the second duration (1-2 years) declined to 144% and an EDR of 6.6 per 1000. Thereafter, there was virtually no excess mortality, and relative cumulative survival at 15 years was 95.6%. However, in the last interval, there were only 19 deaths with tiny exposure; therefore, mortality was not statistically significant. There was no significant excess mortality in any of the last 3 duration intervals from 5 to 15 years (sixth duration is not statistically significant), the MR ranging between 117% and 105%, all ages combined. Observed mortality rates, q, were consistently about the same as the matched population rates, q’, in forth through sixth durations. In the last three 5-year duration intervals, there were only minor, apparently random variations from an MR of 100%, and the MR was not statistically significant in the 15-20-year durational interval.
Papillary Carcinoma, Follicular Variant-PFV (ICD-O-3, 8340)
The term mixed papillary and follicular carcinoma is no longer used, having been superseded simply by papillary carcinoma.9 Nevertheless, there are a total of 38,980 cases in the SEER frequency database from 1993-2013 with designated ICD-O-3, 8340, (topography code C739 for thyroid cancer in the SEER Site/Validation List, September 18, 2015), and therefore, a brief overview of current information is warranted to compare this histologic variant with the invasive thyroid cancer oncotypes in this report. Table 2-Figure 6 case statistics indicate that this histologic tumor accounted for 30,652 cases in females (78.6%), 82.3% in whites, 8.1% in blacks, 8.7% in other races, and only about 0.9% unknown. Mean age at diagnosis for whites and blacks was 49.75 and 49.66 years, respectively. Mean age was higher by about 4 years in males (53.55). Of patients with PCFV thyroid cancer, 71.4% have localized disease at time of diagnosis, 25.8% have regional involvement, 2.1% have distant metastasis, and 0.8% are unstaged. Female incidence begins at ages 1-4 years (3 cases), continues to its highpoint at 45-49 years, and then gradually slopes downward with 181 cases at 85+ years. Male incidence begins at age 5-9 years (13 cases), then slowly rises to its zenith 10 years later (55-59) and then gradually declines to 85+ years with 70 cases. Aggregate average annual mortality and survival results, 1993-2013, are displayed in Chart 4 for the following durational intervals: 0-1, 1-2, 2-5, 5-10, 10-15 and 15-20 years, all ages, races and stages combined.
In Chart 5, expected deaths-d’ exceeded actual or observed deaths-d in all durational intervals and is reflected in mortality ratios of 101% or less. In the Chart 4, EDRs are all basically negative integers and relative survival never dips below 100% at any duration. Mortality and survival in the 15-20-year durational interval is not statistically significant due to the extremely small exposure and number of deaths. Outcomes are quite similar to 20-year follow-up mortality and survival associated with thyroid papillary cancer (ICD-O-3, 8260) noted in Table 6.
Comments and Conclusions
Descriptive epidemiologic characteristics for both papillary and follicular thyroid cancer indicate that it is remarkable to observe a considerable female patient (3 to 1) preponderance to male patients. For papillary and papillary follicular variant (PFV) cancer, incidence for women exceeds that for men by more than 3 to 1. For follicular cancer, incidence in women exceeds that in men by a factor of 2.4. The male-female mean age at diagnosis is a bit earlier for papillary carcinoma (48.2 yrs) than for follicular carcinoma (51.6 yrs). Localized disease in papillary and PFV carcinoma with no significant excess mortality after diagnosis has a very good prognosis. Because nearly two thirds of thyroid cancers are localized, and excess death rate (EDR) is small in patients with regional cancer under age 50, overall excess mortality for all ages also virtually disappeared after 10 years in papillary and follicular cancer. Oxyphilic carcinoma (also called Hurthle cell carcinoma) behave as a slightly more aggressive form of follicular cancer but present similarly. Medullary thyroid carcinoma (MTC) is uncommon, has a large white predominance and a poorer prognosis with non-localized disease than follicular cancer. Anaplastic or undifferentiated carcinoma, which is rare, afflicts those in later decades in life. It is quite deadly in the early durations of follow-up. Nevertheless overall, thyroid cancer remains a formidable health concern in the United States in 2016 with estimated cases of 64,300 and 1980 deaths.
Author's Note:
My profound appreciation to Dr. Richard B. Singer, MD (deceased) for his invaluable collaboration, encouragement and assistance in the initial (unpublished) iteration of long-term comparative mortality in thyroid cancer in 2002.
Contributor Notes