But for the touch of his wife, Mike Campbell might not have found the lump lurking under his left pectoral muscle until it was too late.

For Harvey I. Singer, it took the shooting pain from an old friend's bear hug to finally persuade him to ask his doctor about the change in his left breast.

Neither Campbell nor Singer was prepared for the news that his doctor eventually delivered. Even today, most men would be shocked by a similar diagnosis: Campbell and Singer had breast cancer.

"You could have knocked me over with a feather," said Campbell, of Havertown, a hulk of a man who stands 6 feet, 3 inches tall and weighs 280 pounds. "I said, 'Breast cancer? Are you kidding me?' I was totally shocked."

This year, an estimated 2,200 American men will hear that pronouncement from their physicians. Of those men, about 450 will die from the disease, roughly half of 1 percent of all male cancer deaths, according to Paula D. Ryan, a breast oncologist at the Fox Chase Cancer Center in Northeast Philadelphia.

"Even when guys have symptoms, they ignore it because they don't think they can get this," said Singer, 58, who, with his sister Vicki Singer Wolf, a four-time breast cancer survivor who lives in Worcester, Pa., has founded a website, HISBreastCancer.org, to educate men about the disease.

The incidence of male breast cancer is increasing but remains low, representing only 1 percent of all breast cancer diagnoses. Nevertheless, researchers are studying the differences and similarities between the sexes and their breast cancers.

One approach already yielding information is genetic mapping. Using a 21-gene signature, scientists can create a map of individual tumors, a method that has been validated in large clinical trials of female breast cancer patients. The same process is now being applied to male breast cancer tumors.

"Probing at that level found some similarities and differences," Ryan said. "I think that whole [genetic mapping] trend is going to help us better define male breast cancer at the molecular level."

While male cases bear many similarities to female breast cancer, there are important differences. For instance, most female breast cancers are lobular; that is, they start in the glands that produce milk. Most male breast cancers are ductal, or in the ducts that carry the milk to the nipple.

In a study presented at the American Society of Breast Surgeons annual meeting in May, Jon Greif reported that men with breast cancer were more likely to be black than female patients; men's tumors were larger at diagnosis; and men were older at diagnosis: 63 compared with 59 for women.

Male breast cancer typically begins as a painless, firm mass just below the border of the areola, the ring of color around a human nipple, said Ryan. Because the male breast is smaller, the mass tends to be more centrally located. Nipple retraction and changes in the skin or lymph nodes under the arm are tell-tale symptoms. But most men, like Campbell, are usually unaware that they have the disease.

"I had no symptoms of anything," said Campbell, 62, whose cancer was diagnosed four years ago. "My wife had her hand at the 12 o'clock position above my left breast and said, 'What's this?' I said, 'What's what?' You could feel an obvious lump. I had no idea that it was there. That's what kills a lot of men. We don't know that we can get it."

Campbell had none of the risk factors: enlarged breasts, liver disease, family history, and obesity, among others. But doctors have known there is a direct link between breast cancer and inherited mutations of the tumor suppressor BRCA1 and BRCA2 genes. Men and women with the BRCA1 or BRCA2 mutation, especially of Jewish ancestry, have a much higher risk of breast, ovarian and prostate cancers.

Wolf warned her brother that he could be carrying the mutated genes. "I shoo-shooed her," said Singer, who grew up in Northeast Philadelphia but now lives in Rochester, N.Y. "I saw a change in my left nipple. It folded over and inverted, a telltale sign."

It wasn't until a few weeks later that a friend grabbed him in a bear hug and he felt a shooting pain. He realized that something was seriously wrong. He felt around his breast and discovered a lump under his nipple.

After his diagnosis in 2008, Singer scoured the Internet for information. He found very little. Singer vowed to change that, and in 2009 he and Wolf launched HISBreastCancer.org (The HIS stands for Harvey Irwin Singer.) In the last year, the site has averaged 2,200 page views a month.

The purpose of the website, Wolf said, is to educate the public and medical professionals.

"Doctors don't understand" male breast cancer, Wolf said. "A man with a family history should have a baseline ultrasound because you have family members with breast cancer."

The website has another purpose: removing the stigma and embarrassment of being a man with breast cancer. "There is a stigma, and men are embarrassed by it," Singer said. "This still holds some macho value that you are a guy with a woman's disease. That is a major problem for some men."