CT Scans & Cancer Risk

December 20, 2009 by Robert Wascher  
Filed under CT Scans, Cancer, Cancer Prevention

Welcome to Weekly Health Update



 

“A critical weekly review of important new research findings for health-conscious readers”




HAPPY HOLIDAYS FROM WEEKLY HEALTH UPDATE!

 

 

 

CT SCANS & CANCER RISK

 

 

CT (computed tomography) scanners have revolutionized the practice of medicine since they were first introduced into routine clinical practice in 1974.  CT scanners utilize a rotating x-ray device to create hundreds of individual images that can then be reconstructed into a complex three dimensional view of the body by computers.  Current generation CT scanners are able to image the entire human body within seconds, and these high definition images provide physicians with an incredibly detailed view of the organs and tissues deep within us. 

 

CT scanners have become an indispensible diagnostic tool within virtually every medical and surgical specialty, and an estimated 75 million CT scans are now performed annually in the United States, alone.  As the popularity of these complex and powerful diagnostic imaging machines has continued to grow, so has their use for clinically dubious reasons.  For example, routine scans of the heart, and its coronary arteries, have, increasingly, been used for “screening purposes” in patients without any clinical evidence of heart disease.  Likewise, there has been an explosion in the number of private radiology imaging centers offering fee-based “body scans” for clinically healthy people who are interested in having their internal organs examined for any early signs of diseases that can be detected by CT scans.  Another area of concern regarding the use of CT scanners is that physicians have become so dependent on these machines, and the exquisite images of the human body that they provide, that many (if not most) doctors have a very low threshold to order CT scans as a routine part of their diagnostic work-up of patients.  (For example, in my own specialty of Surgery, the diagnosis of appendicitis is now routinely made with a CT scanner, rather than by the traditional method of the surgeon’s clinical evaluation of the patient.) 

 

While CT scanners have become essential diagnostic tools, they also expose patients to much higher doses of radiation than most conventional x-ray examinations.    It has long been known that exposure to radiation increases the risk of developing cancer, and that the risk of developing cancer is proportional to the dose of radiation received by patients.  (Based upon recent estimates, it has been estimated that at least 2 percent of all cancer cases may be caused by prior exposure to medical x-rays.)  Moreover, there is no known “safe” dose of radiation in terms of radiation-induced cancer risk.  As if this was not already bad enough, there has been a growing concern regarding the actual dose of radiation that is being delivered to patients from CT scanners across the country, as there is a great deal of variability in the radiation dose settings being used among different CT scan imaging facilities.  (This alarming point was recently brought to the public’s attention when it was revealed that Cedars Sinai Medical Center, a prestigious private hospital in the Beverly Hills area, was being investigated after multiple patients who had undergone CT scans of their brain there began to notice that their hair was falling out.  Authorities subsequently determined that these patients had received grossly excessive radiation doses during their scans.)

 

 

Two very important public health studies have just been published in the Archives of Internal Medicine, and the findings of these two related studies have significantly raised the level of concern regarding the current use of CT scanners among public health experts. 

 

The first of these two studies quantified the amount of radiation dose delivered to 1,119 patients for 11 common types of CT scan examinations that were performed at 4 different hospitals in the San Francisco area.  In addition to calculating the radiation doses received by these patients, the authors also estimated the probable lifetime cancer risk associated with these CT scans.  As the Cedars Sinai case has already shown, there appears to be considerable variability in the amount of radiation used at different institutions to conduct the same exact type of CT scan.  However, the sheer magnitude of this variability in radiation doses, as measured by these researchers, is both mind-boggling and disturbing.  Not only was there an enormous difference in radiation doses associated with performing the same exact type of CT scan between the 4 different institutions that were studied, but significant radiation exposure differences were also present within each individual institution when performing the same type of CT scan examination on different patients.  When the researchers had finished their calculations, they noted an almost unbelievable 13-fold difference, on average, in radiation exposure for the same type of CT scan between the highest and lowest observed radiation doses for each individual type of CT examination. 

 

Based largely upon cancer incidence data collected after the Hiroshima and Nagasaki atomic bombings, this clinical study’s researchers calculated that an estimated 1 in 270 women who underwent a CT scans of their coronary arteries at age 40 will eventually develop cancer as a direct result of these CT scans (versus 1 in 600 men), while 1 in 8,100 women who underwent CT scans of the brain at age 40 will develop cancer from these scans (versus 1 in 11,080 men).  For men and women who underwent CT scans at age 20 (instead of age 40), the projected lifetime risk of CT scan-associated cancer was nearly double the projected risk of the 40 year-old patients. 

 

The findings of this study indicate that the variability in radiation exposure between hospitals for the same type of CT scan examination is much greater than was previously believed.  Perhaps even more surprising was the finding that identical CT scan examinations performed within a single hospital also subjected patients to significantly different amounts of radiation exposure.  Finally, the calculated range of radiation exposure for CT scans revealed that, in general, patients are receiving far higher doses of radiation from routine CT scans than has generally been appreciated.  (For example, a single CT coronary artery angiogram delivers the same amount of radiation as 310 chest x-rays!)

 

The second research study used public health data to estimate the average number of radiation-induced cancers caused by CT scans in the United States.  Based upon current CT scan use, these researchers predicted that approximately 29,000 future cases of cancer could be expected to arise from CT scans performed in 2007 in the United States, resulting in approximately 15,000 deaths due to cancers caused directly by CT scans!

 

These two studies are eye-openers that should cause all of us, physicians and patients alike, to reconsider the benefits versus the risks of each and every CT scan that is considered before such scans are performed.  Although most CT scans are performed because they offer vitally important clinical information on patients that could only otherwise be obtained by surgical exploration, too many CT scans are still being ordered and performed for far less compelling reasons (one of them being, unquestionably, the tendency of many physicians to order multiple unnecessary tests on patients as part of their practice of “defensive medicine,” in the absence of tort reform throughout most areas of the United States…).  Moreover, the striking variation in CT-associated radiation doses, and the unexpectedly high level of these radiation doses in general, points to the need to improve standardization and compliance at every one of the thousands of institutions in the United States that operates a CT scanner.


As a dedicated cancer specialist, I am already well aware of the potential for radiation-induced cancers, and I have, for many years, tried to be very selective in ordering CT scans on my patients.  In cases where I can gather the necessary clinical information without resorting to radiographic imaging, then I try to avoid obtaining any form of x-ray examination (including CT scans).  In other cases, where I must obtain some sort of imaging examination, then I will often initially use ultrasound or MRI studies in place of CT scans, when appropriate.  Even so, the dramatic findings of these two studies suggest to me that all physicians need to further decrease their routine use of CT scans whenever possible. 

 

   


Disclaimer: As always, my advice to readers is to seek the advice of your physician before making any significant changes in medications, diet, or level of physical activity

Dr. Wascher is an oncologic surgeon, a professor of surgery, a cancer researcher, an oncology consultant, and a widely published author

 

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Soy Isoflavones Reduce Breast Cancer Recurrence Risk

Welcome to Weekly Health Update



 

“A critical weekly review of important new research findings for health-conscious readers”


SOY ISOFLAVONES REDUCE BREAST CANCER

RECURRENCE RISK

 

 

Regular readers of this column are already aware of the controversy surrounding soy isoflavone intake and breast cancer risk.  As happens frequently in clinical research (unfortunately), contradictory research findings have made it difficult to understand the true relationship between dietary soy intake and breast cancer risk (if one exists).  There is, for example, both laboratory and clinical data suggesting that a diet rich in soybean-derived products may be associated with a lower risk of developing breast cancer.  At the same time, because genistein and other dietary isoflavones are known to weakly mimic the effects of estrogen, there has been some concern that a diet rich in isoflavone “phytoestrogens” may increase both the risk of developing a new breast cancer and the risk of developing a recurrence of a previous breast cancer.  (In fact, there is data from laboratory research studies showing that genistein can indeed fuel the growth of human breast cancer cells growing in culture dishes, when exposed to high concentrations of this soy-derived isoflavone.)

 

A growing body of public health research, primarily from Asian countries where tofu and other soy-based foods are frequently consumed, appears to link increased soy consumption with a decreased lifetime breast cancer risk, particularly when soy-based foods are consumed during adolescence, during the time when development of the female breast is most active (Soy & Breast Cancer Risk).  (Interestingly, there is also recent research suggesting that soy products might also reduce the risk of prostate cancer, which is another hormonally driven cancer:   Genistein & Prostate Cancer Cells, Dietary Soy & Prostate Cancer Risk.)

 

Although epidemiological research is, increasingly, suggesting that a diet rich in soybean-derived foods might lower a woman’s lifetime risk of developing breast cancer, many breast cancer experts have remained apprehensive regarding dietary isoflavone intake in women with a prior history of breast cancer, in view of the estrogen-like effects of these “phytoestrogens.”  As I have already noted, there is considerable research data available to suggest that soy-derived isoflavones can, at least under certain laboratory conditions, stimulate estrogen-sensitive breast cancer cells to grow and divide.  These research findings have left many oncologists feeling uncomfortable in recommending soy-based foods to their breast cancer patients.  Now, a newly publish public health study in the Journal of the American Medical Association suggests that soy-based foods may actually reduce the risk of breast cancer recurrence, and death due to any cause, in women who have previously been diagnosed with this very common form of cancer.

 

In this study, which was performed in Shanghai, China, 5,042 female breast cancer survivors (ages 20 to 75 years) were followed for an average of almost 4 years.  All of these patient volunteers underwent detailed surveys regarding their lifestyle habits, including their diets.  These patients, who were originally diagnosed with breast cancer between 2002 and 2006, were surveyed at 6, 18, 36 and 60 months following their original diagnosis with breast cancer.  

 

The results of this study indicate that the breast cancer survivors who consumed the greatest amount of soy-based foods in their daily diets were 32 percent less likely to experience a recurrence of their breast cancer when compared to the women who consumed the least amount of soy-based isoflavones.  Moreover, the women who consumed the greatest amount of soy were also 29 percent less likely to die, from any cause, when compared to the women who consumed the least amount of soy-derived foods.

 

A particularly interesting and unexpected finding of this study was that both women with estrogen sensitive breast cancers and women with tumors that were not sensitive to estrogen appeared to experience a significantly decreased risk of breast cancer recurrence if they frequently consumed soy products.  Another important finding of this study was that women who were taking the estrogen-blocking cancer treatment drug tamoxifen also appeared to enjoy a reduced risk of breast cancer recurrence with higher levels of dietary soy intake.  Additionally, the researchers noted that high levels of soy intake appeared to be about as effective in reducing the risk of breast cancer recurrence as the breast cancer prevention drug tamoxifen, alone.

 

The results of this very important study mirror the findings of the only other prospective clinical study that has looked at the impact of soy-based foods on breast cancer recurrence (the “Life After Cancer Epidemiology,” or “LACE,” study).  The LACE study, which was performed in the United States, followed nearly 2,000 breast cancer survivors for, on average, more than 6 years.  In the LACE study, women who were taking tamoxifen, and who also consumed the highest amount of soy-based dietary isoflavones, were 50 percent less likely to develop a recurrence of their breast cancer when compared to women who reported the lowest consumption of soy-derived foods.

 

As I have pointed out previously, epidemiological research studies based upon dietary surveys are susceptible to several types of bias which, in turn, can cause researchers to draw the wrong conclusions.  In this case, however, there are now two large prospective cohort studies that have reached essentially the same conclusions (albeit with a rather limited duration of patient follow-up).  Both studies strongly suggest that high levels of soy-based isoflavones in the diet may be able to significantly reduce the risk of breast cancer recurrence.  Based upon the findings of this large Chinese study, the apparent cancer risk reduction effect associated with high levels of soy intake also appears to benefit premenopausal and postmenopausal women, as well as women who are taking the estrogen-blocking drug tamoxifen, women with estrogen-sensitive tumors, and women with (counter-intuitively) estrogen-resistant tumors.

 

In view of the limited duration of patient follow-up in both of these clinical breast cancer studies, as well as the limitations of survey-based epidemiological research in general, I would like to see updated data from both of these studies after at least 10 years of patient observation before I would be willing to tell my breast cancer patients that they should significantly increase their dietary soy intake.  On the other hand, the rather compelling data presented by both of these clinical research studies will also make me less anxious when any of my breast cancer patients decide, of their own accord, to increase their intake of soy-derived isoflavones.

 

 

Note:  Weekly Health Update is currently undergoing an extensive upgrade to better serve its tens of thousands of health-conscious readers around the world.  Beginning in January 2010, newly archived columns will be available by selecting the “Archives” tab on the right side of your screen (all archived columns prior to January 2010 will continue to be available by selecting the “Archives 2007-2009” tab at the top of the screen.)


 


Disclaimer: As always, my advice to readers is to seek the advice of your physician before making any significant changes in medications, diet, or level of physical activity


Dr. Wascher is an oncologic surgeon, a professor of surgery, a cancer researcher, an oncology consultant, and a widely published author

 

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Salt (Sodium) Intake, Stroke & Cardiovascular Disease

December 6, 2009 by Robert Wascher  
Filed under Nutrition, diet, health, heart disease, stroke

Welcome to Weekly Health Update



 

“A critical weekly review of important new research findings for health-conscious readers”


 

Salt (Sodium) Intake, Stroke & Cardiovascular Disease

 

 

Table salt consists of the elements sodium and chloride, both of which are essential for life.  There is a great deal of clinical research suggesting that more than 5 to 6 grams of salt intake per day (which is equal to 2 to 2.4 grams of sodium)  is associated with a significant increase in the risk of developing high blood pressure which, in turn, is associated with a significantly increased risk of stroke and cardiovascular disease.  Unfortunately, in most countries, the average daily salt intake for adults is considerably greater than 6 grams per day.  Moreover, in many countries of the world, the average daily adult intake of salt is a whopping 12 grams per day, or almost 5 grams of sodium per day. 

 

In the United States, the American Heart Association (AHA) currently recommends no more than 2.3 grams of sodium intake per day (equivalent to 5 grams, or about one teaspoon, of salt per day).  At the same time, the AHA also states that the ideal daily intake of sodium should actually be about 1.5 grams per day but, in an acknowledgment regarding the high intake of salt-rich processed foods in the United States, the AHA considers the 2.3 gram per day dietary sodium target to be more “realistic” for Americans.

 

There is considerable public health research data suggesting that the reduction of average daily adult salt intake, to 6 grams per day, or less, would result in a significant lowering of blood pressure in both people with and without high blood pressure.  Based upon these research findings, some public health experts have predicted that lowering the average daily salt intake below 6 grams per day could reduce the incidence of stroke by almost 25 percent, and the incidence of cardiovascular disease by almost 20 percent.  Unfortunately, there have not been any large-scale prospective, randomized, placebo-controlled clinical research trials performed to validate these estimates.  On the other hand, there have been multiple short-term prospective public health trials that have followed groups (cohorts) of patients in terms of their dietary intake of salt and the incidence of stroke and cardiovascular disease events.  Now, a newly published research study, in the British Medical Journal, has performed a meta-analysis of 13 of these “prospective cohort” studies, encompassing a total of 177,025 patient volunteers, with average durations of patient follow-up ranging from 4 to 19 years.  (Meta-analysis is a method of combining the data from multiple different clinical studies into a single “super-study,” in an effort to improve the validity of the resulting data, as well as the conclusions that are reached from such data.)

 

Among these more than 177,000 patient volunteers, there were 11,000 “vascular events” observed, including stroke and heart attacks (myocardial infarctions).  When the incidence of these vascular events was analyzed, along with dietary salt intake, the patients with the highest daily salt intake were observed to experience a 23 percent greater risk of stroke, and a 17 percent greater risk of cardiovascular disease, when compared to the adults who consumed less salt on a daily basis.

 

The increasing consumption of salt-rich processed foods throughout both the developed and underdeveloped countries of the world has been pushing daily salt intake to ever higher levels, with many Western countries reporting average daily adult salt intake of nearly 10 grams per day.  In other countries, and most notably in Asia and Eastern Europe, dietary practices that include a high concentration of heavily salted foods have pushed daily salt intake into the 10 to 12 gram per day range for the average adult.

 

The World Heart Federation estimates that there are 5.5 million annual deaths from stroke across the globe, and an additional 17.5 million annual deaths from cardiovascular disease.  Based upon the increased incidence of stroke and cardiovascular disease predicted by this meta-analysis study, even a rather modest decrease in the average adult daily salt intake, to the World Health Organization’s target of 5 grams per day, should result in 1.25 million fewer deaths per year from stroke and nearly 3 million fewer annual deaths from cardiovascular disease around the world.  Needless to say, this is a tremendous potential public health dividend from a rather simple alteration in our dietary habits.  (On the surface, reducing our daily salt intake would appear to be a rather simple goal.  However, the more complicated reality is that to achieve even the World Health Organization’s rather liberal target of 5 grams of salt per day, our entire food chain would have to be comprehensively reexamined and overhauled.) 

 

The world’s increasing consumption of highly-processed foods, which often contain high levels of salt as a preservative, are largely responsible for the high levels of salt intake in the developed world (in addition to a preference for salt-cured foods in much of Asia and Eastern Europe).  In the United States, the sodium content of most processed foods is readily available on food packages.  Unfortunately, most restaurants in the United States have not been as forthcoming about the sodium content of the food on their menus (as well as other important nutritional information), and so it continues to be very difficult to determine the actual salt content of much of what we eat here in the United States and, indeed, throughout much of the world.

 

 

 

Note:  Weekly Health Update is currently undergoing an extensive upgrade to better serve its tens of thousands of health-conscious readers around the world.  Beginning in January 2010, newly archived columns will be available by selecting the “Archives” tab on the right side of your screen (all archived columns prior to January 2010 will continue to be available by selecting the “Archives 2007-2009” tab at the top of the screen.)


 


Disclaimer: As always, my advice to readers is to seek the advice of your physician before making any significant changes in medications, diet, or level of physical activity


Dr. Wascher is an oncologic surgeon, a professor of surgery, a cancer researcher, an oncology consultant, and a widely published author

 

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