Is there a relationship between stomach cancer and colorectal cancer?

Sometimes. Certain genetic cancer syndromes have increased risk for cancers in multiple areas of the GI tract. If you have multiple family members who have had cancer discuss it with your family physician and see if meeting with a genetic counselor would be the right thing to do.
Sometimes. Cancers are basically accumulations of cells that have mutated and no longer "follow the rules". There are chemical ways that this can happen, and there are stomach and colon cancers that share many mutations. There are some syndromes, most notably fap (familial adenomatous polyposis), that are associated with both stomach and colorectal cancer.

Related Questions

Is there a connection between stomach cancer and colorectal cancer?

Maybe. But only in the rare case of non-hereditary polyposis colorectal cancer is there an association. It is an extremely rare inherited condition (nhpcc).
No? In practical terms there is not. Gastric or "stomach cancer" is more common in japan, iceland, chile and costa rica were "volcanic" soil is common and diet is rich in fruit and vegetables. Colon cancer is common in societies (like usa) were diet is poor in fiber & diet relies on more refined foods (from canned or processed food). I guess one can metastasize into the other. Exceptions do exist.

How rare are stomach and / or colorectal cancer occurances in teenagers?

Very rare. If there is a family history, certain stomach, and especially colon cancers can develop in the young, especially if their parents died very young from the same tumors. There are known genetic predispositions for these types of cancer.
Fewer than 1% Of stomach or colon cancers occur in teens. Familial genetic risks may increase personal risk, but it is not a national problem.

Lower ab pain for weeks, freq. Urge to go, rumbling in my stomach. Lrg skin tags on rectum 24f can this be colorectal cancer? Other cancers run in my family

Possible.... ..But I think other things are far more likely. You should see your doctor for a thorough exam.
Nonspecific. Colorectal cancer is often asymptomatic until he later stages, which is why screening colonoscopy generally starting at age 50 is so important. So if you haven't had one yet, see. Gi doctor to set one up.
Unclear. The skin tags usually are not a sign of cancer. But having these symptoms for weeks is abnormal. You should see your friendly primary care doctor to find the cause of these symptoms.

What can increase the chances of a teenager getting stomach and/or colorectal cancer?

Extremely rare. It is extremely rare that a teenager would get stomach or colon cancer. Increased chances would more likely involve colon cancer, with in an inherited familial colonic polyposis syndrome.

Colorectal cancer surgery and colostomy? Why does the doctor have to do a colostomy as part of colorectal cancer surgery? What is it exactly (a hole in my abdomen?) and how long will I have it?

Some. Some ostomies are for ever and other temporary. For low rectal cancer a temporary may be use to proted the new conection alowed to be healthy. If the cancer is to low involving the muscle to control the stool a penmanented ostomy is need. Yes a stoma is a open in you abdomen that alowwed a small portion of teh bowel to come out and it is cover by a ostomy bag.
Not. Not all colorectal cancer surgeries requires a colostomy. A colostomy is more often needed during an emergency operation (when there is no time to clean the bowel properly before the operation), like perforation or obstruction of the bowel caused by the tumor, that can create contamination and infections inside the abdomen. In those conditions putting the bowel together could be very risky and lead to failure of the operation, and doing a colostomy would help to control the contamination and prevent further infection. Commonly, after four to six weeks it is then safe to put the bowel together. On the other hand, if a colorectal cancer is detected in an early stage and no emergency situations are present, the bowel can be prepared properly and put together with less chances of having a complication. However, even in ideal conditions, some times the surgeon can find situations during the surgery which are concerning for possible complications (like poor blood supply to the bowel) and a temporary colostomy is performed to protect the bowel connection and let it heal safely without the passage of stool. Finally, some colostomies are permanent, depending on the location, the size, or the extension of the tumor to other organs.