I had the opportunity recently to participate in a Twitter chat on the topic of colorectal cancer awareness. The chat was intended to bring attention to a nationwide campaign called “80 by 2018” designed to increase colorectal cancer screening rates to 80% of the population over the next 4 years. If it is successful, we should see a decline in both incidence and deaths from this disease.

But I am haunted by two of the comments I tweeted during the session chat that won’t leave my conscience:

“As a doc, you don’t forget the patients you couldn’t help. And you celebrate those you did.#CRCawareness is key #80by2018”

“Let’s remember that screening doesn’t help everyone, so don’t forget the need for more research in understanding #CRC #80by2018”

While we celebrate the opportunity to save more lives with screening, we cannot ignore or forget those for whom screening for colorectal cancer (or other cancers, for that matter) couldn’t or didn’t make a difference.

Let me share a couple of stories with you. These are obviously people I have remembered over the years and who have had a continued impact for me personally.

The first person was a woman in her 70s. She was a pleasant lady who had had a prior stroke but was still very functional and otherwise in good health. I would see her in my office periodically during the year for routine medical care. During that time — well before electronic health records were available — I would keep a piece of paper in the front of my chart to record when certain periodic tests like cholesterol and mammograms were done. I would enter the date, and indicate if the test was completed. Colon cancer screening was one of those tests on the list.

Every year, we had the same discussion: Please get screened. And every year, the answer was no. I would explain why I thought it was important, and she would nod her head and say, “No.”

She wouldn’t use the stool cards to test for blood, and I was not permitted to do any form of internal exam. And every year, over about 7 or 8 years as best I recall, I would make a little note in my file that we had that discussion. Until …

The call came from her son, who had been incredibly supportive of his mother through the years. She had some blood in her stool. I had her come in immediately, and a rectal exam confirmed their observation. She refused a sigmoidoscopy or colonoscopy, but said she would have a barium enema. My heart sank when I saw the report: There was an extensive cancer in the sigmoid colon, just above the rectum. And further testing showed it had spread.

You can imagine the tragic end to this story. She had surgery, but the cancer was advanced. She declined any further treatment and subsequently died at home.

One moment that I have never forgotten is bringing her son from the waiting room to my office to tell him about the x-ray results. I was terribly saddened. Something I could have found had not been found. She never gave me the opportunity. I told him about the results, and then showed him my chart. At that moment, he was more a force of care for me than I could be for him.

“Doctor, I know you talked to her every year. You don’t have to show me the chart. She told me every time she came for a visit. She just wouldn’t listen.”

There are other stories, different stories, that show us another side of this terrible disease.

My patient was a young man, in his late 30s. Hardworking, family, responsible. All the “right” things. During a routine examination I found that he had an iron deficiency anemia. Men at that age don’t have iron deficiency anemia. It is a signal that something may be terribly wrong, and it was: Colonoscopy showed a cancer in the right side of the colon (those cancers tend to bleed slowly over time). The good news was that the cancer was reasonably small and could be resected. We did an evaluation which at the time included a CT scan of the abdomen. It was completely negative. No spread was evident.

About 10 days later, after he got his work squared away, he was admitted for removal of the cancer. I got a phone call from his surgeon asking me to come to the operating room immediately. The CT scan was hanging on the wall, and it was absolutely clean. But the abdomen was not. There were large lesions in the liver that were cancerous. These would not have been missed on the CT scan. His disease was rampant throughout his body. Treatment options in those days were limited, and there was nothing we could do.

And then there is the conversation I had with someone that saddened me to my core. A person at high risk, who had polyps resulting in multiple follow-ups with colonoscopies. She was religious in keeping her appointments, and her doctor screened her in accordance with well-accepted guidelines. And now she had a cancer that was large, had penetrated through the bowel and leaked into the abdomen. The cancer had a particular genetic marker that was consistent with its aggressive behavior. Screening did not prevent this tragedy.

Why do I tell you these stories? Why was I haunted by my comment that we celebrate those we help, and shed tears in our memory for those we could not?

There is much we can do in this country to reduce the incidence and death of colorectal cancer if we did what we already know. We have already made considerable progress, but we can do more. And screening is a large part of how we can get there. For many patients, screening may catch a polyp early before it becomes cancer or detect a cancer when it is in its earlier stages. If we could get more people screened for colorectal cancer, there is no question we could save many more lives.

But then there are those who don’t fit the usual picture. They may develop the disease at a young age, they may have a family history, they may have a genetic mutation in their cancer. Whatever the reason, their cancer is the type that screening may not help.

So, as I said, we celebrate our successes. We celebrate those where we can prevent the disease or catch it early or provide treatment that significantly improves the chances of survival. But we also mourn those where screening could not make a difference, where we need to better understand the reasons why the cancer was so malicious and so devastating that there was never a chance.

We must never forget that no matter how successful we are for so many — whether it be breast, lung, colorectal or any other cancer — there remain far too many where early interventions simply don’t work. And in the memory of those who never had a chance, we must move forward with every resource we have to find the answers, and offer hope to those who follow.

J. Leonard Lichtenfeld is deputy chief medical officer, American Cancer Society. He blogs at Dr. Len’s Cancer Blog.