Re: PET Scans & False Positives
I'm sorry to read about your 86-year-old mother having these problems. I know it is schocking to have occur. I went through this last fall with my 95-year-old mother. She happen to have a 5cm "benign" tumor in her stomach.
The father of a good friend had stomach cancer at age 90 and had 80% of his stomach removed. He's one of the fortunate few who was cured, recently celebrating his 97th birthday. He lost a ton of weight, after his 80% gastrectomy, but this was probably serendipitous. He always had a truly terrible, high fat diet, because his stomach was shrunk, his intake of bad food was reduced, which probably contributed to his longevity.
Physicians increasingly use endoscopic ultrasound (EUS) to assess gastrointestinal and lung diseases. EUS can provide detailed, cost-effective, nonsurgical assessment of certain diseases. Because it can be technically demanding and complex, an experienced endoscopist should perform EUS.
EUS involves passing a thin, flexible tube (endoscope) through a patient's mouth or anus. A small ultrasound transducer in the endoscope produces sound waves that create a viewable image of surrounding tissue. Physicians use EUS to examine the lining and walls of the upper and lower gastrointestinal tract and nearby organs such as the pancreas, liver, and gallbladder.
Physicians may use two main types of EUS transducers. One is a radial imaging device that produces a 360-degree, cross-sectional image (also called a "slice"). The other is a curved linear array instrument that uses Doppler and pulse Doppler ultrasound that can guide a fine-needle aspiration (biopsy) of lymph nodes and tumors. Physicians choose the transducer that will produce the image they need to assess a patient's problem.
Another kind of ultrasound allows very high-resolution imaging of the surface of the gastrointestinal tract. Physicians use this kind to help determine the size of small nodules and how deeply the nodules involve the wall of the GI tract.
When combined with fine-needle aspiration, EUS is a minimally invasive, state-of-the-art alternative to exploratory surgery to remove tissue samples from abdominal and other organs. Physicians also use EUS to guide pseudocyst drainage, injections, and painkilling treatments.
Since PET images biochemical activity, it can accurately predict whether a tumor is benign or malignant, thereby avoiding surgical biopsy when the PET scan is negative. Conversely, since a PET scan images the entire body, confirmation of non-local metastasis can alter treatment plans. In some cases this may mean a change from surgical intervention to chemotherapy.
However, with chemotherapy, patients would certainly have a better chance of success had their cancer been "chemo-sensitive" rather than "chemo-resistant" where it is more apparent that chemotherapy improves the survival of patients, and where identifying the most effective chemotherapy would be more likely to improve survival. Some surgical resection or at least a "tru-cut" biopsy of a fresh "live" tumor specimen could be most beneficial. Testing the tumor first to fine the most synergistic (cooperative) anti-cancer agents against the cancerous cells.
PET is extremely sensitive in determining the full extent of disease, especially in lymphoma, melanoma, breast, lung, colon and ovarian cancers. Confirmation of advanced metastases allows the physician and patient to more accurately decide on how to proceed, especially if the patient is against extraordinary measures or decides not to undergo the rigors of chemotherapy in the time they have remaining. PET improves the quality of a patient's remaining time in these cases.
Research indicates that PET is playing a growing role in tracking the effectiveness of chemotherapy and evaluating early response to an empirically-selected drug. The level of tumor metabolism is compared on PET scans taken before and after chemotherapy. A successful response seen on a PET scan frequently precedes alterations in anatomy and would therefore be an earlier indicator of tumor shrinkage than would be seen with other diagnostic modalities. The same assessment applies to tracking the effectiveness of radiation therapy.
According to Dr. Val Lowe, a nuclear medicine specialist at the Mayo Clinic, no study has PET proved inferior to either CT or MRI. In staging cancers of the head and neck, comparative studies report a slight statistical advantage for PET over CT or MRI, with some published reports documenting high sensitivity and specificity for PET. For example, FDG PET is more sensitive in detecting primary tumors (PET sensitivity, 89% to 100%; CT or MRI sensitivity, 68% to 92%), and lymph node involvement (PET sensitivity, 74% to 100%; CT or MRI sensitivity, 36% to 94%).
Being that your mother is having empirically-directed chemotherapy, I hope the agents are effective against her cancer cells. Possible indications of whether chemotherapy benefits esophageal cancer patients can be provided by PET imaging, but the biggest difference is that with PET imaging, you give the patient potentially toxic and ineffective drugs and wait six to eight weeks and then make tumor measurements.
And then give more potentially toxic and ineffective drugs and wait another six to eight weeks and repeat measurements. You still have the patient getting potentially toxic and ineffective treatment and then you still have to wait weeks until you could try Plan B. And you may promote the onset of clinically acquired multi-drug resistance.
You measure the drug effects on tumors in the patient (one treatment at a time), rather than in the laboratory where as many as twenty-thirty treatments can be done to see which one works best. The outcome for metabolic responders and non-responders in PET imaging is basically what is going on with "functional profiling" in cell culture assays, showing what patients are benefiting from what drug agents, "before" they are put in the patient.
These drugs are given based on how large populations are likely to respond to a treatment. However, doctors don't treat populations, they treat individual patients. Because of this, doctors give treatments knowing full well that only a certain percentage of patients will receive a benefit from any given medicine.
A chemo-induced gene mutation can happen when the original chemo received does not work. The cancer comes back. When it does this, the cancer comes back more aggressively. The mutagenic effects (changes in form) of chemotherapy on a genetically-unstable tumor, drives the tumor into a state of more aggressive behavior.
Cancers that are a product of these genetic mutations release cells from the usual controls of proliferation and survival, making them so much harder to fight it. Following this mutation, the cancer cells acquire the ability to proliferate without the normal restraints.
As the cancer grows, it may infiltrate and destroy the surrounding tissue, and metastasize by penetrating into blood vessels, lymph nodes, and body cavities. Distant metastasis via the bloodstream may affect virtually any organ (the lungs, bones, liver, adrenals, and even the brain).
Pet Scans in Oncology: [url]http://cancerfocus.org/forum/showthread.php?t=3466
Gregory D. Pawelski
Last edited by gdpawel : 10-16-2012 at 05:43 PM.
Reason: corrected url address