There may be few obvious signs of breast cancer.

Breast cancer is the most common cancer in women (besides skin cancer), affecting about 12% or 1 in 8 women in her lifetime. Men aren't immune either. The American Cancer Society reports that more than 2,600 men are diagnosed with breast cancer each year.

Many times, there's no symptom or sign that indicates breast cancer is present. For many patients, a breast cancer diagnosis only comes about via a routine mammogram or ultrasound meant to screen for this common malignancy, "which is why screening is so important," says Dr. Melissa L. Pilewskie, a breast surgeon oncologist at Memorial Sloan Kettering Cancer Center in New York City.

But in some cases, there are signs that something is going on with your breasts. Stay aware and visit your doctor if you develop any of the following five signs that you might have breast cancer.

1. A lump

Perhaps the most common sign of breast cancer is the development of a lump in the breast or under the armpit. But just because you develop a lump doesn't mean it's definitely cancer. The American Cancer Society reports that 80% of breast lumps are noncancerous and can be caused by a range of different conditions.

It should also be noted that lumps and bumps in the breast are very common. Often, these hard areas are caused by fibrous tissue or cysts. Cysts are simply fluid-filled sacs within the breast tissue, and they may go away on their own. Your doctor might drain a large or uncomfortable cyst with a needle.

Although cancerous lumps tend to be more irregular in shape, the only way to know whether any lump is dangerous or benign is by asking your doctor, who will typically order a mammogram or an ultrasound to get a closer look at the lump, and then possibly a biopsy to check the tissue itself.

"It's certainly important to have a general awareness of the breast, your breasts, and to seek evaluation for any abnormal lumps or bumps or painful areas," says Dr. Harold Burstein, institute physician at Dana-Farber Cancer Institute in Boston and associate professor of medicine at Harvard Medical School.

It's best to get any new lumps in the breast checked by a doctor as soon as possible.

2. Unexplained size changes

Women's breasts can change in size and shape based on hormonal fluctuations that occur normally during the menstrual cycle. But any substantial changes to the size or shape of one or both breasts could be cause for concern, particularly if these breast shape changes "produce differences between the breasts," says Dr. Michele Carpenter, program director for the breast program at St. Joseph Hospital's Center for Cancer Prevention and Treatment in Orange County, California.

While it's very common and completely normal for women to have one breast that's larger than the other, any changes to size or shape of the breast should send you to the doctor for evaluation.

3. Dimpling, puckering, redness, flaking, itching and other skin changes

An aggressive but rare form of breast cancer called inflammatory breast cancer can sometimes create changes to the skin of the breast, creating a dimpled or puckered effect on the skin. Often, these changes are described as making the skin look like the surface of an orange and may be described as "peau d'orange."

Inflammatory breast cancer also sometimes causes pain, swelling and redness in the breast. While pain is typically not associated with most types of breast cancer, tenderness or discomfort in the breast is worth getting checked out as it could signal other issues related to hormones or other conditions.

Skin changes can also be a sign of another rare form of breast cancer called Paget's disease. But skin changes, such as a rash or bruise, can also be caused by simple dermatitis, eczema or a trauma, such as being hit with a ball. If such explanations are not readily available, it's best to get any redness or discoloration checked out by a doctor.

4. Nipple discharge

Carpenter notes that "nipple discharge that's spontaneous" has a "low chance" of being cancerous, but should be checked out.

If you're not breastfeeding but you develop spontaneous discharge from the breast -- whether that's watery or thick, clear or another color -- "it's important to seek evaluation," Burstein says.

Such abnormal nipple discharge could indicate cancer, but it also can mean that there's a hormonal problem or thyroid disease. Spontaneous lactation or nipple discharge can also be a sign of an infection or a side effect of certain medications such as birth control pills. In all cases, talk to your doctor.

5. Changes to the nipple

If the nipple becomes painful, retracts, flattens or inverts so it looks like it's turned in toward the breast, those changes can all be signs of breast cancer. If the skin around the nipple or areola -- the darker pigmented skin surrounding the nipple -- become scaly or dry like they've been sunburned, that can be a sign of trouble.

Be aware of your breasts and what's normal for you.

Breasts are made up of:

-- Fat.

-- Fibrous connective tissue.

-- Glandular tissue.

-- Nerves.

-- Blood vessels.

-- A complex network of milk-producing lobules and ducts.

As such, breast tissue can naturally feel lumpy, bumpy and uneven, and there's wide variation in what's normal from one person to another. It's important to become familiar with what's normal for you and to speak up if something changes or seems abnormal. If in doubt, check it out.

What to do if you find any signs of breast cancer

First, don't panic. As noted, many of these changes to the shape, size or appearance of the breast may be caused by benign conditions or normal hormonal fluctuations. And even if it's cancer, Carpenter notes that "breast cancer is a highly curable disease. There are more breast cancer survivors in the U.S. than any other cancer except skin cancer survivors."

Next, call your doctor and set up an appointment. Carpenter encourages you to "make sure you're up to date on your mammogram. If you're young and don't get regular breast imaging, see your doctor so they can start the process of imaging and referral if needed."

Even after the symptoms have been investigated and resolved, it's best to keep up with routine breast health, Carpenter says. "If you find breast cancer earlier, you have a better chance of surviving and will need less aggressive treatments. Survivorship is improving every year because of better treatments and diagnostic testing. We're understanding more about breast cancer than we ever knew before."

5 signs you might have breast cancer

1. A lump.

2. Unexplained size changes.

3. Dimpling, puckering, redness, flaking, itching and other skin changes.

4. Nipple discharge.

5. Changes to the nipple