Mammograms, PSA Tests, and PAP Smears: The difficulty in screening for cancer

Within a few years, cancer is on track to overtake heart disease as the #1 cause of death among Americans, and one out of every two of us is expected to be diagnosed with cancer at some point in our lives.  Cancer is extremely prevalent, and a big question is how best to fight it.  History has shown us that the survival rates are much higher when treating cancer in its earliest stages, and so one main focus of our healthcare system is to diagnose cancer as soon as possible.

I think almost everyone has had at least some experience with cancer screening.  We are always told to check ourselves for suspicious lumps or weird pains - things like breast or testicular self-exams.  We also undergo screening during our annual checkups.  Mammograms (breast cancer), prostate-specific antigen tests (PSA, prostate cancer), colonoscopy (colon cancer) and PAP smears (cervical cancer) are the most common.  Other tests that can be used are chest x-rays (lung cancer) and MRI or CT scans (for anything else).

Yet if you read the news, there seems to be a lot of controversy over what kind of tests are necessary.  Recently, the US Preventative Services Task Force advised that healthy men should not receive PSA testing.    The same task force has also advised against mammography for women under the age of 50.  At first glance, this may seem odd - if there is a test that can diagnose cancer, why not perform it all the time?  

A good test must be able to accurately detect when cancer is present.  But what many people don't consider is this: what happens when the test is wrong?  In this post, I'll go over some of the science of screening for cancer, and hopefully explain why the guidelines are set the way they are.

Read more after the break.

Is there more cancer today?

Roughly 1 in 2 Americans will be diagnosed with cancer at some point in their lives.  Some of us are screened for cancer with what seems like an ever-increasing frequency.  Cancer is one of the most researched and most publicized illnesses.  Some would say that awareness of cancer is at an all time high, and this often raises many questions.  Have humans always gotten cancer?  Is cancer more prevalent now than it was before?  Why do our lives seem so full of cancer now?

A brief history of cancer

Cancer arises when cells in the body lose their ability to regulate cellular division.  When this happens, a cell begins to divide out of control - dividing more and more until there are so many cancer cells that it impedes the normal function of the body.  Cellular division is part of life, and some people argue that cancer is as old as life itself.  In fact, recent evidence suggests that dinosaurs got cancer over 65 million years ago.

We know that cancer in humans has been around for some time as well.  The ancient Egyptians and Greeks both described cancer in their medical writings, but didn't have much in the way of treatment besides amputation.  Yet until the 20th century, cancer was just a blip on the healthcare radar.

In 1971, Richard Nixon and Congress began the effort which is now known as the "War on Cancer."    This was a response to the massive increase in the rate of cancer deaths since the turn of the 20th century.  Money has poured into cancer research and treatment since then, yet despite our best efforts, cancer is still predicted to overtake heart disease as the #1 cause of death among Americans within the next few years.

Why is cancer so prevalent?  If we analyze the rise of cancer in the 20th century, we learn a lot about the American medical system, as well as how cancer works.

Read more after the break.

Which College Teams are Over-Ranked in Pre-Season Polls?

As we near Thanksgiving, I like to look back on the college football pre-season rankings.  It always makes for good comedy.  One thing (maybe the only thing?) I admire about the BCS is that they wait until the teams have actually played some games to attempt to rank them.  Pre-season rankings tend to be based on a mix of historical success, recruiting strength, and public perception.  Here is where we stand as of week 13:

              2012 AP Poll
  PreSeason                 Week 13

1 USC 1 Notre Dame

2  Alabama   2 Alabama

3  LSU   3  Georgia

4  Oklahoma   4  Ohio State

5  Oregon   5  Oregon

6  Georgia   6  Florida

7  Florida State  7  Kansas State

8  Michigan   8  LSU

9  South Carolina  9  Texas A&M

10 Arkansas  10 Florida State

11  West Virginia  11  Stanford

12  Wisconsin  12  Clemson

13  Michigan State  13  South Carolina

14  Clemson   14  Oklahoma

15  Texas   15  UCLA

16  Virginia Tech  16  Oregon State

17  Nebraska  17  Nebraska

18  Ohio State  18  Texas

19  Oklahoma State  19  Louisville

20  TCU   20  Michigan

21  Stanford  21  Rutgers

22  Kansas State  22  Oklahoma State

23  Florida   23  Kent State

24  Boise State  24  Northern Illinois

25  Louisville  25  Mississippi State

Is "Gerrymandering" Responsible for the House Majority?

The 2012 election was, by all accounts, a victory for the Democrats.  President Obama was re-elected in spite of the economic downturn that took place during his first term, and the Democrats picked up seats in both the House and Senate.  However, the GOP maintained its majority in the House of Representatives, 234-201 (assuming the current leaders in the 4 un-called races go on to win).

It was predicted for some time that the House wouldn't switch hands, so many people didn't pay much attention to the races.  But there are some excellent election datasets out there - for instance, the Google Elections data browser (edit: it seems as though the google elections data browser has been taken offline).  And if you browse through the results of the Congressional elections, you might see some surprising things.

Case in point: Florida's 5th District.

Fig. 1: Gerrymandering in Florida?  It seems like Democrats are packed into the 5th District, allowing nearby districts to be won more easily by Republicans.

How dangerous are the new TSA scanners?

Every blog needs a test post. This is mine. If anyone happens to ever read this introduction - hello! I work in Radiation Oncology, and I like explaining things to people. I also like analyzing otherwise mundane things to find interesting information. I'm a scientist first and a writer second, so you will probably come away from this being more informed than entertained. But hopefully a little of both.

What follows is a post of mine originally featured on smallerquestions.org. 

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I think everyone has seen them by now - the new scanners that the Transport Safety Administration has installed at airports all over the US. As the “radiation person” in my group of friends, I get a lot of people asking about them. “How much radiation do they use?” “Are they safe?” “Should I opt out of the scan and get a pat down?” The answers to the second two questions are subjective, but several studies have been done to evaluate #1. The first studies, done by the TSA itself, met with a lot of criticism from various groups. The study made the assumption that the radiation distributed itself uniformly across the body, which turns out not to be the case. Several members of the UCSF faculty wrote a letter of concern (pdf link), asserting that the risk was underestimated because most of the radiation from low-energy x-rays is deposited in the skin. And since there are nearly 1 billion airline passengers in the US each year, any small increase in cancer risk could add up to significant harm to the overall population.

First, we need to make a distinction. There are two types of these new scanners: “millimeter wave” and “backscatter.” The two airports I use the most, Atlanta and Denver, both have millimeter wave scanners. These use the same radiation that your cell phone does, which don’t have enough energy to break chemical bonds in your cells. The backscatter scanner uses so-called “ionizing radiation”, which is the same x-rays used for dental scans or CT imaging. These photons have enough energy to break chemical bonds, and can cause DNA mutations that lead to cancer (more info in Sarah’s post about EM spectrum). From here on I use “radiation” to mean “ionizing radiation” for the sake of brevity.

The radiation dose delivered during one of these backscatter scans has been evaluated in several venues, but the most recent is a paper by Hoppe and Schmidt out of Marquette University. Although the abstract reads like an episode of Ghost Hunters (“Voxelized phantoms of male and female adults and children were used with the GEANT4 toolkit to simulate a backscatter security scan.”), in my opinion these types of papers tend to be very dry (a voxelized phantom is just a computer model of an object receiving radiation). However, the conclusions can be profound – “For a full screen, all phantoms’ total effective doses were below the established 0.25 μSv standard, with an estimated maximum total effective dose of 0.07 μSv for full screen of a male child.” (!)