Cancer is an insidious killer. Often, it sneaks up on people and gets a stranglehold on their health before they even realize that something is wrong. Yet survival often depends on how early cancer is caught — and that means knowing the signs a tumor is present.

“The bottom line is the earlier cancer is detected, the better the chance of a successful outcome.” says Carolyn “Bo” Aldigé, founder and president of the non-profit Prevent Cancer Foundation.

“If the cancer is contained in the organ where it started, it’s much more amenable to being treated with surgery, chemotherapy, radiation and/or immunotherapy.”

While some cancer symptoms — such as a lump in a breast or bloody stools — will get most people rushing to their doctor, others are more subtle. Another expert warns that any persistent health issue may be trouble.

“I think ‘persistent’ is a key word,” notes Dr. Therese Bevers, medical director of the Cancer Prevention Center at MD Anderson Cancer Center in Houston. “If you have a symptom that persists, and you don’t know what the cause of it is for sure, you need to get it checked out.”

Here are several potential early warning signs of cancer that you should never ignore:

Persistent cough or hoarseness: These are common symptoms of respiratory infections, but if they don’t go away after three or four weeks, get checked out. They could be warning signs of lung, laryngeal, esophageal, or thyroid cancer.

Unexplained weight loss: You may think it’s great that you’re finally dropping some pounds without even trying, but Bevers warns: “That doesn’t happen in healthy adults. Go see your doctor if you lose 10 pounds or more.”

Difficulty swallowing: “Head and neck cancers can affect mucus membranes, and you need that lubrication to swallow,” Aldigé tells Newsmax Health.

Extreme fatigue: Low energy can be a symptom of a variety of health problems ranging from nutritional deficiencies to sleep apnea. But it’s also common to many forms of cancer, particularly stomach, colon, and leukemia.

Changes in bowel movements: Besides bleeding, if stools are narrower or looser than what is normal for your, or you start going more frequently or at different times of the day, it could be a sign of colorectal cancer. “Persistent constipation is another red flag,” Bevers tells Newsmax Health.

Enlarged belly veins: If you’re suddenly able to see blood vessels through the skin of your abdomen, it could signal liver cancer. “It’s a rare symptom,” says Bevers, “but liver cancer often doesn’t give any early warning signs at all.”

Itching: Itchy skin has many causes, and it’s rarely cancer-generated. But unexplained itchiness could signal certain types of blood cancers or lymphomas.

Bloating: “A lot of women have a feeling of being constantly bloated, and that is something doctors will often shrug off,” says Aldigé. “Then it turns out they have ovarian cancer. Bloating is much more symptomatic of ovarian cancer than other cancers.”

Changes in breasts: Lumps aren’t the only sign of breast cancer. The puckering of nipples, pain, tenderness, discharges, and the scaling or itching of skin are all potential harbingers. And it’s not just women who are at risk. About one in a 1,000 men get it too.

Persistent earache: This could signal oral cancer. That’s because sensation at the back of the tongue and in the ear are served by the same nerve. Other signs of oral cancer include mouth ulcers that won’t go away and a lump in the neck.

Chronic heartburn: A little indigestion never hurt anyone, but when you have it all of the time it could be a symptom of esophageal cancer.

Changes in moles: “Pay attention to moles,” says Aldigé, noting abnormalities can indicate skin cancer. “Any changes in size or shape, or any mole larger than a pencil eraser, should be checked out. It’s not just changes but also any new mole, especially if it’s dark. That’s concerning to me.”