This is too much; the way the medical field treats the elderly is criminal!

I expect the GP relied on the opinion of the radiologist after the CT scan.

Are you absolutely sure you want your grandmother to go through a colonoscopy and biopsy? Assume for a moment that the cancer diagnosis is confirmed. What would be the options then?

I should think it through, is all I'm saying.

It is likely the CT was read by a radiologist (easily done remotely).
Do you want to but your grandmother (with Alzheimer's) through a coloscopy and biopsy? To what end? Surgery? Chemo? 
First, I'd find out FOR SURE, who read the CT scan, then I'd go with hospice and pain management.

Usually the scan results are read by a Radiologist and sent to the requesting doctor.
The radiologist could be anywhere in the country and the local doc is just reading the report and passing the results on to you.
But, Grandma is up there in age and may not want any intervention, plus getting her to go thru a colonoscopy and general anesthesia could be worse than the cancer.
Please consider what the procedure could do her before making decisions.

lizsdaughter207, it isn't criminal how the medical field threats the elderly. It is more likely common sense. You mentioned your Grandmother has progressively worse Alzheimer's. Right there it is limited on what doctors can and cannot do.

Most of today's colonoscopy are done with anesthesia. Even that short time being under would have an effect on Grandmother's mind. She would come out more confused then ever. Is that fair to her?

If Grandmother has surgery, she will yet again be under anesthesia which will rush her Alzheimer's to yet another stage. Also need to consider the physiological changes that accompany aging, such as diminished organ function, which will affect how chemotherapy is metabolized.

My own Mom had bladder cancer, had it for a number of years, every year she went in for routine testing. Her Urologist told me that my Mom would probably pass from something else. Sure enough years later it was something else. Glad I didn't put her through the terrible fear of surgery, and then chemo at her late age. She was doing quite well without it.

Countrymouse is right. The doctor at my mom’s facility wasn’t worth much either. He was there once a week for over 100 patients and only saw those who were borderline being sent to the ER. But, there was a staff of very competent nurses, aides and therapists. I relied on them for observing my mom and alerting me if something needing addressing. 

If she hasn’t had those tests yet, if she were of sound mind, I can almost guarantee you she’d say no. Us old people get to the point we don’t want to be messed with, especially with things like a colonoscopy. My mother avoided that like the plague for 20 years and finally told the doctor outright, “I’m not having one!” She had gone through a mastectomy at the age of 84 and just decided she’d had it, and if cancer didn’t get her, something else would.

Most CT scans go thru two readings. Standard protocol is a reading done by a radiologist with the medical group who performed the procedure. Then a second reading by a radiologist with a second group. CT’s are not read by a patient’s GP. If the CT is read as positive it means that the CT indicated a mass or tumor that is emitting radiopaque luminosities indicating malignancy. I would not insist on a colonoscopy or other invasive procedures.

I agree, the radiologist probably told the doctor its cancer. They can be wrong though. My mom has COPD and after her annual scan, the radiologist told her lung dr that she has an aggressive form of lung cancer! The dr didn't tell mom that but he told her she needed a biopsy right away. Biopsy showed NO CANCER! But that said, you have to consider your grandmothers age and her alzheimers. Do you really want to put her under anethesia? and if it is cancer, do you know what chemo and radiation will do?

Have you ever had a colonoscopy? Do you know what the prep is like?

I would advise a palliative care consult. Some colon cancers grow very slowly and can be watched. Others are already blocking the bowel, which can be an extremely painful way to die. There is not one answer to the course going forward. A palliative care professional can help you sort out your options.

I'm sorry that you've gone through this very frustrating experience. Let's hope the comedy of errors is over!

Has your mother had the conoloscopy and biopsy?