Wednesday, May 20, 2009

What is a PET Scan?

I am describing the PET scan first to help you understand what it is &, second, to inform you of its significance.

What is it?
PET (or positron emission tomography) is a medical imaging tool. It is used to detect and to monitor cancer. The device used looks like a CT scanner, and, in fact, the scans I have simultaneously perform both a CT & a PET scan.

A PET scan is very different from an ultrasound, X-ray, MRI, or CT. Unlike these imaging technologies which merely confirm the presence of a mass; they cannot determine whether a tumor is still active once it is determined that it is malignant. A PET scan can distinguish between benign and malignant disorders.

PET can help physicians effectively pinpoint the source of cancer. It can detect abnormalities in cellular activity, generally before there is any physical change. It can visualize a tumor in size from 7mm to 1cm depending on the location. This is smaller than the other technologies, which typically detect tumors that are 1cm or larger.

Cancer cells have a much higher metabolic rate than other cells. One characteristic is that cancer cells need higher levels of glucose for energy. This is the biological process PET measures.

As part of the procedure, a form of slightly radioactive glucose (sugar) is injected into the patient about 45 minutes prior to the scan. The cells of the body absorb this sugar, which releases atomic particles called positrons. These positrons combine with electrons in the body to produce gamma rays. As gamma rays leave the body, they are detected by a special camera. The recorded emissions provide a three-dimensional map of how glucose is used throughout the body. The images from the scanner contain varying colors or levels of brightness that help physicians identify abnormalities, such as the presence of cancer. For example, cancerous tissues use more energy and absorb more sugar than healthy tissues. For this reason, these malignant areas appear brighter than normal tissues on PET scan images.

You may wonder why radioactive glucose is used. Cancer cells demonstrate a 3 to 5 fold increase in glucose uptake compared to healthy cells. That is what it means when the sentence above says, “they have a much higher metabolic rate than other cells.” Another way to say it is to say, cancer is a sugar-feeder. Scientists call it an “obligate glucose metabolizer.” Cancer cells primarily use glucose for fuel.

You can slow cancer growth by lowering the amount of fuel available to the tumor cells. This is the reason my diet eliminates all sugar. It also eliminates or restricts foods with a high glycemic index. I eat fruits but not bananas because they are too quickly converted to glucose. I do not eat refined grains for the same reason. When I have whole or multi-grains I must have them with a source of protein to keep my blood sugar level from rising significantly. I do not eat vegetables that grow below the ground, except garlic & onions, for the same reason. Raw carrots are permissible, as they are not quickly converted to glucose.

As you can imagine, it makes my decisions easier when I know that to eat the right foods I am feeding my body, but to eat the wrong foods I am feeding the cancer. I certainly don’t want to feed the cancer cells!!

What is its significance?
My first PET scan was done December 18, 2007. At that time, I had a malignant lymph node that was just over 2 cm, in my left armpit, removed. I had a 2 cm biopsy of 2 calcifications in my left breast, which did not appear suspicious on the digital mammogram or ultrasound, that was malignant, & the surgeon did not get clean margins. A CT scan in September indicated that there were some nodules on each lung, but I was advised to have them rechecked in 6 months. Dr. Patel, my oncologist, decided to order a PET scan to make a final diagnosis with respect to the stage of my cancer. From the above description, you can see that a PET scan is the only technology that can pinpoint all sites where cancer is present. This PET scan revealed that my cancer has metastasized (spread) from my left breast to 4 lymph nodes under my left arm, multiple lymph nodes along the mediastinum (behind the breast bone), & several small nodules on both lungs. The fact that the cancer has spread to a major organ causes it to be classified as stage IV.
By May 2008, I had 3 PET scans & my tumor marker had dropped in response to the medication I started taking December 27, 2007. Here is the progression of my numbers:
12/10/07 --- 211
PET scan 12/18/07 (staged cancer)
12/27/07 --- 291.3
Started aromatese inhibitor (AI) 12/27/07 It takes 1 month to take full effect.
1/30/08 --- 580.8 same day, apt. with Dr. Powers & changed my diet drastically
PET scan 2/19/08 (scan showed slight improvement)
2/27/08 --- 389.7
PET scan 5/6/08 (additional improvement)
5/14/08 --- 126.7

Dr. Patel explained that the tumor marker number showed a definite correlation with the PET scan results – it increased until the medication was started & took full effect, then it dropped & the scan results showed improvement -- so that it was not necessary to undergo the additional radiation of the PET scan every 6 or 8 weeks, if the tumor marker results are valid. The tumor marker is determined from a blood sample. (A complete explanation of a tumor marker is in a July 2008 blog.)

Normal for the CA 27.29 tumor marker is 38.8 or below. Since my blood work indicates that it has been in this range since December 2008, Dr. Patel decided he really does not know what the cancer is doing. The only way to know is to do a PET scan. This PET scan will show us what is going on & also reveal whether or not the tumor marker is, as we have assumed for this past year, reporting a valid picture of the state of my cancer.

My PET scan 5/12/09 shows the tumor marker numbers are, indeed, valid! At this time, it shows activity in only ONE lymph node under my arm, and that activity is described as “barely visible & is probably not likely clinically significant at this time.” That’s as close as I can imagine to remission!! Praise God! Thank you for your prayers! There is NO activity in any of the other lymph nodes or nodules! Praise God!!!!

My ulcerative colitis (UC) previously showed up as a false positive. Guess what? It didn’t show up on this scan! In fact, I have been able to eliminate one of the medications I take for my UC. I was taking 2 pills a day of one medication & 12 a day of another. I have completely eliminated the medication that I was taking 12 pills a day. It’s incredible! I am healthier today than I was the day I was diagnosed with stage IV metastatic breast cancer! God is AWESOME!

1 comment:

Bláithín said...

Patti, you've explained all this so well!! Again, I'm so amazed at your progress...but then, I really shouldn't be amazed as it is clearly God at work!