How Rare Is Sarcoma Really?

[Charts still under construction.]

By Joan Darling

Everyone who has been affected by the family of cancers known as sarcoma knows that it is rare.  For example, when one of the Sarcoma Alliance board members was diagnosed with the rhabdomyosarcoma (rhabdo for short) as a teenager, her family was told that about 6 children in a million come are diagnosed with this aggressive cancer.  A recent news article about a child battling the same type of pediatric sarcoma, made it sound even rarer, stating that this aggressive cancer strikes one child in a million.

These low numbers seem to be supported by the National Cancer Institute SEER (Surveillance Epidemiology End Result) statistics.  This is the most authoritative study on incidence of cancer in the United States, and the SEER data indicate that among children under the age of 20, on average about 5 children out of every 1,000,000 will be diagnosed with rhabdomyosarcoma each year.  Certainly it is not a common disease.

Table 1

[Table coming soon.]

Rates are per 1,000,000Source: http://seer.cancer.gov/csr/1975_2009_pops09/results_merged/sect_29_childhood_cancer_iccc.pdf

Indeed, almost everything one reads about sarcomas emphasizes their rarity.  Among no age group are they common.  The following table shows that the estimated number of new sarcoma cases in the U.S. in 2012 was about 14,000, approximately 1 percent of all cancers. Rare, right?

Table 2

 [Table coming soon.]

http://seer.cancer.gov/csr/1975_2009_pops09/results_single/sect_01_table.01.pdf

Sarcomas are relatively more common among children than in adults.  Between 1,500 and 1,700 U.S. children are diagnosed with a bone or soft tissue sarcoma each year making up about 15 percent of pediatric cancers (compared to that 1 percent of adult cancers) but pediatric cancers themselves are rare and make up only 1 percent of cancer cases (Sarcoma Progress Report).

But is a child’s risk of getting rhabdo really as uncommon as single digits in a million?  If that’s the case, why do any of us affected by sarcoma know many others who have been similarly affected?  Do the statistics, as Mark Twain implied, mislead?

How Many People in the U.S. Have Sarcoma?

The rarity of sarcomas potentially has been a barrier to attracting researchers and raising funds, therefore perhaps it is time to look at the statistics in a different way.

An oft-quoted fact about prostate cancer is that one of every 6 men will develop it sometime during their lifetime.  In the same vein, one out of every 8 women will develop breast cancer during their lifetimes.  These rather startling numbers make these cancers seem omnipresent, and have been a valuable rallying point for raising funds for research.

These statistics for prostate or breast cancer are given as the risk over an entire lifetime, but up until recently it was hard to find comparable lifetime risks for developing sarcomas.  The 1,700 children or 14,000 total numbers of sarcoma cases, and the five in a million for rhabdomyosarcoma, all represent the risk for a single year.  But obviously an average human lifespan is much longer than a year.  Just as the risk for prostate or breast cancer is given as a lifetime risk, the lifetime risk for sarcoma is in reality a great deal larger than these numbers indicate.

It’s true that only about 400 children a year in the US are diagnosed with rhabdo, and thus the numbers are in the single digits in a million.  But it is also true that one of every 330 children will get cancer by the age of 20, and that rhabdo is about 4 percent of childhood cancers.  That means that about one of every 8,500 children will get rhabdo by the age of 20.  And a handful of people will get it later in life.

This really reflects the incidence of rhabdo – one in every 8,500 children will get rhabdo.  This is quite different from the six in one million statistic that I had heard.  The explanation is the difference between the chance of getting it in any one year, and the cumulative risk of getting it at any time during childhood.  Each year, the odds of a child getting rhabdo are about six in a million.  Multiply that by the 20 years of “childhood” and the odds of a child getting rhabdo are about 120 in a million, or 12 in 100,000, or just about one in 8,500.

This cumulative number is important because sarcomas such as rhabdo are not like chicken pox or a broken leg – they don’t have a short time frame, and they most certainly don’t have a point at which you can be certain you are healed or “cured”.  Many people live with their disease for years, being treated periodically with surgery or radiation.  Even for those who have no evidence of disease, there is always the fear that the disease will recur, and this time will be much less likely to be successfully treated.

The same goes for adult sarcomas.  SEER indicates that based on rates from 2007-2009, 1 in 304 men and women will be diagnosed with cancer of the soft tissue and 1 in 1270 with bone and joint cancers during their lifetime.  In the U.S. population of 300 million, this means that about 1 million people have been or will be affected by sarcoma.

http://seer.cancer.gov/statfacts/html/soft.html and http://seer.cancer.gov/statfacts/html/bones.html

 “When” counts as much as “How Many”

This number might surprise you, but another sarcoma statistic increases its impact on society still further, and that is the age at which sarcomas are diagnosed.  Cancers that affect younger people have disproportionately large impacts on society, because the younger the victim, the more potential there is to contribute to society.  For example, despite the relatively small number of cases of childhood cancer, an extremely large number of years of life are lost if a child does not survive.  The graphs below from SEER demonstrate this effect.  The left chart below illustrates that despite the rarity of childhood cancer, an astounding 94,000 person-years of life are lost each year to childhood cancer, just for children up to the age of 14.

Figure 1

[Information coming.]

http://seer.cancer.gov/csr/1975_2009_pops09/results_merged/topic_year_lost.pdf

The reason is explained in the right chart. That chart shows that for each child who does not survive cancer, a staggering 71 years of life are lost on average.  Compare this to the 9 years lost on average for prostate cancer, or the 19 years for breast cancer.   The loss of a child to cancer means the loss of an entire life-time, the loss of a potential and promise that society can never regain.  Although all cancer is terrible, and research is needed to cure it all, on average prostate cancer strikes men and breast cancer strikes women later in life.  It is a loss to society when anyone’s life is cut short, but the death of a child from cancer results in an incomparably larger loss of the potential to contribute to society.

It’s hard to find similar statistics for adult sarcomas as most adult cancer statistics are given by site of cancer and not by type of cancer.  As a result, sarcomas are not lumped together in an easy way to analyze.   But it is very likely that if sarcomas were broken out separately, they would also show a disproportionately large loss of person-years.

The reason is that, unlike many other cancers, sarcoma is a disease of young and old alike, and thus the same principal should apply – the person-years lost to deaths from sarcoma should be disproportionately large.   The young age at which many adult sarcoma patients are diagnosed also means that, just as for childhood cancers, there are many years in which there can be an accumulated large number of sarcoma survivors, and a the potential for a large number of person-years lost when someone dies from sarcoma.

The NCI SEER (Surveillance Epidemiology and End Results) project has compiled data that show the risk for developing cancer at a specific age.  The SEER data indicates that about a third of soft tissue cancers (not exactly the same as, but most comparable to soft tissue sarcomas) and over half of bone sarcomas are diagnosed in people under 45 years of age.  In comparison, less than one-tenth of all cancers occur in this age group (Table 3).  Even more startling, the table shows that over a third of bone sarcomas and almost a fifth of soft tissue cancers are diagnosed in people under the age of 35, compared to less than 4 percent of all cancers.

Table 3

http://seer.cancer.gov/csr/1975_2009_pops09/results_merged/topic_age_dist.pdf

Another way of looking at this is to consider the MEDIAN age at which cancer is diagnosed.  The median is a type of average which represents the age at which half the people are younger at diagnosis and half are older.  As can be seen in Table 4, the median age of all cancer diagnoses in the U.S. is 66 years, whereas it is 41 years for bone cancers and 58 for soft tissue cancers.  Thus, the average age of sarcoma diagnosis is considerably younger than the age of most cancer diagnoses.

Table 5

http://seer.cancer.gov/csr/1975_2009_pops09/results_merged/topic_med_age.pdf

The importance of the young age at which many sarcomas are diagnosed has many important implications.  For survivors, there are many years of worry about relapse or dealing with side effects of treatment.  Survivor health issues are particularly true of children with sarcomas who required multi-modal therapy including relatively high doses of chemotherapy and radiation.

For those who do not survive, there is the tragedy of dying far before their time, leaving behind parents, spouses, children, friends, co-workers and the potential that will never be fulfilled.

And there is at least one other implication for research into improved cancer treatments.  Young people diagnosed with cancer usually relatively healthy otherwise, and do not have a lot of other diseases that can complicate clinical trials for new treatments.  They should be prime candidates for inclusion into clinical trials.

This has several consequences which make sarcomas more important to public health than their numbers alone would indicate.  For one thing, as indicated for childhood cancer, the number of person-years saved by increasing survival is disproportionately large for cancers that strike relatively young people.  And sarcoma strike relatively young people.

For another thing, because many sarcoma patients are young, with the exception of their sarcoma they are relatively healthy.  They should be ideal candidates for research studies, as they are less likely to have other health issues which may compromise the ability to try intensive treatments.

Why the Way we use Statistics is Important

It is possible that funding for sarcoma research and educational efforts will never be adequate unless advocates present numbers that truly reflect the impact of this disease on our society.  For example, the few in a million number makes it sound as though there are only a few families dealing with one phase or other of the rhabdomyosarcoma experience in the US, when really there are many, many more.  If a typical family has two adults and two children, then about one in every 4,000 families will have a child with rhabdo.

And remember that rhabdo makes up a quarter of pediatric sarcomas, and pediatric sarcomas make up about 15 percent of all sarcomas.  Therefore, about ONE IN EVERY THOUSAND FAMILIES WILL HAVE A CHILD WITH A PEDIATRIC SARCOMA, and ONE IN EVERY 150 FAMILIES WILL INCLUDE SOMEONE WHO IS BATTLING OR WHO HAS BATTLED WITH SARCOMA.

Bottom line, is sarcoma rare?  Maybe not so rare after all.