Consider this stunning statistic one in eight women will develop invasive breast cancer during her lifetime. Little wonder so many of us make the annual trek to get a mammogram. Thinking that if... See More
Consider this stunning statistic one in eight women will develop invasive breast cancer during her lifetime. Little wonder so many of us make the annual trek to get a mammogram. Thinking that if something is detected surely a biopsy will determine whether it's cancer or not. But if you think a -- is as simple as black and white think again. And Judy Valencia story we'll show you in tonight's Nightline investigates. -- It's not something most of us look forward to but just like 37 million other women who get a routine mammogram every year. It was now my turn. I was lucky enough to be -- one of New York city's premier hospitals Mount Sinai Medical Center. 700 miles away in Saginaw Michigan Judy Valencia has been vigilant about getting her mammograms. My sister had breast cancer and my mother had breast cancer. And -- three can't can't comprehend breast cancer. -- -- got good news about my mammogram. -- wasn't so lucky. I went for -- -- -- -- share and then after that they fattened for a pact. And it's very paintball based on that biopsy Judy was told she had cancer. There's nobody questions that I have me and get to double check -- the women most get a second opinion says doctor release support. One of the nation's leading breast surgeons who works at mount Sinai as you've -- breast center and you have. A woman come to you and whose that I have been diagnosed breast cancer and then it is be ready for surgery and discover she didn't have a you know. Absolutely I mean we. For -- never even get close to an operating room. But we see patients all the time they come in with their diagnosis from the report saying breast cancer. We passed -- -- -- to -- pathologists who sends me back a report in days later saying. Don't agree this is not cancer and it's very clear cut that it's not. And -- that's probably one of the most critical pieces of information that's when knowing even gets near an operating room until those slides are reviewed. So we're in the pathology laboratory where we processed tissues. That come from surgery or from biopsies and doctor -- were. Why -- is one of the country's leading breast pathologists that. Ironically doctor -- -- says that the cost mammograms have become so much better at detecting smaller and smaller lesions. Diagnosing breast cancer can actually be more difficult these days he showed me an example. And this is core -- When certain to the radiologist. Was an irregular solid advance so this is a lump in someone's breast but not detectable by the woman problem that's correct. No question your mind about this -- not absolutely this is an easy case easy to diagnose. But all cancers are not disdain so this is a tough one yes why. Because it changes -- very subtle every pathologists even every trained pathologists who looked at this might not see at the same way that's correct. How often you get presented with a -- like this one which is really sort of if they -- every day. Everyday there. That that's a very common occurrence and my. Forty you're going to perform surgery someone. You want a better reading of that biopsy and -- it's just having gone to some general -- yes that does -- and gallstones and I think it's it's not only go. How can a person who does one mastectomy. A month. Do it as well as someone who does ten a week these are things that are subject to interpretation. And more expertise in making that interpretation is better. But local hospitals don't have -- breast pathologists and surgeons. In 20061. Highly regarded study warned the Arab -- in diagnosing breast cancer could be as high as 4%. Which means as many as 101000 women each year could be misdiagnosed. Which brings us back to Judy Valencia. After her diagnosis she was told she had two choices a lumpectomy to removed a cancerous portion. Wore a mastectomy to remove her entire breast. Panic because of her family history Judy chose the most extreme course she decided to removed both -- the one with cancer. And one without. I just wanted to to be done I didn't I don't have to worry about. Going through half again as painful and is disfiguring and is. Radical. Step is it is it -- it seems like okay. Case closed. I'm breast cancer -- exactly do you what cancer I was cancer free and there was not radiation to be had -- keen on. I was great and it -- game. -- -- -- and Richard have been married for 39 years. Richard says he supported his wife's decision to remove both -- I watched. Number her relatives. -- solely because of -- that's -- when she discussed about having. Double mastectomy than adults went along with -- -- they have my wife here. He. Didn't -- -- about my paper or. In the months that followed Judi says she couldn't get paperwork from the hospital for her insurance so she hired a lawyer. Her lawyer suspected something was wrong and -- -- original biopsy for a second opinion to doctor bloc allies back in mount Sinai. -- doctor Bly -- is opinion. Judy never had breast cancer. I want to the line Arens said he had goodness in him -- army and the argument again -- -- and -- says. He said you -- cancer free you have no cancer never had seen wearing me. Because it wasn't just that you didn't have cancer is that you ignore had -- -- -- -- and that's right Judy had both breasts removed and was now being told she'd never had breast cancer and a hall. -- lawyer Greg -- has not says it was a mistake that should never have happened. The pathologists. At this. Institution had doubt about what they were looking. When they wrote the report they didn't have clarification. They gamble. -- -- -- -- There are people who. Do get misdiagnosed. Based on someone not having that expertise to know what they're looking it is important stack the odds in your favor putting together a team. That deals with this a lot and this is what they eat sleep and breathe he's taking care of patients with breast cancer or would think they might have breast cancer. That's how -- stack the odds in your favor. -- Valencia's second opinion came too late but she says she's now telling her story in hopes that other people. We'll learn from her -- deal I have an have to live with the mistake for the rest of your life. It happened profane. But I can have my grandchildren and -- here and -- -- -- The doctors at mount Sinai say a set opinion does not have to cost a fortune often is just a matter of sending your slides. To -- next.
This transcript has been automatically generated and may not be 100% accurate.