Even by the broadest definition possible — abnormal cell growth — there are more than 100 different “types” of cancer, depending on where in the body that growth first occurs.

Similarly, though cancer often leaves its sufferers racked with pain, these symptoms will vary depending on factors such as the cancer's location and exact cause (to say nothing of the many cancer treatments that also cause painful side effects). In light of this, let’s take a brief look at four of the most painful cancers around, in no particular order, as well as why they hurt so much.

Stomach Cancer

Currently the fifth most commonly detected cancer worldwide, with nearly one million new cases diagnosed annually, stomach cancer often becomes especially painful because of its clandestine nature.

Most people with stomach cancer will only find out about it after the cancer has spread past its origin site. So while the earliest symptoms may include abdominal pain, weight loss, and heartburn, more advanced cases can vary in the pain and damage they cause, depending on where it spreads. Often, the cancer spreads to the intestines, which leads to excruciating bowel obstructions that may require surgery to relieve. While cases overall have been declining and survival rates have improved, stomach cancer remains among the most fatal — as of 2008, it’s estimated that only around 30 percent of diagnosed patients will survive past five years.

Pancreatic Cancer

Yet another type that spreads elsewhere in the body with little warning, pancreatic cancer is invariably fatal once it reaches this advanced, metastatic stage.

Though it can theoretically spread anywhere, it most often spreads to the bone and lymph nodes. And the most common source of pain in these patients comes from the bones closest to the prostate, such as the pelvis, hips, and lower spine. The cancer ravages them, leaving a aching, dull or numbing pain that makes walking difficult.

Prostate cancer is also among the more likely types to cause a condition called metastatic spinal cord compression. In these cases, the wayward tumor puts an intense pressure on the spinal cord, which if untreated usually leads to severe and worsening lower back pain, problems going to the bathroom, and numbness and tingling throughout the body.

Breast Cancer

While breast cancer tumors are rarely themselves very painful, advanced cases often spread to the nervous system. The resulting tumors can damage the nerves and cause lingering, intense neuropathic pain. Indeed, many cancers and common treatments like chemotherapy can cause this sort of nerve damage, and it’s estimated 40 percent of cancer pain is neuropathic in nature.

“Trying to explain the pain is difficult, like hundreds of needles inside my head,” said one patient with neuropathic pain who was interviewed for a 2009 study in The BMJ. “I ended up trying to relate it to other pain I have suffered over my lifetime. For instance, ear infection at its worst, very bad migraine, tonsillitis. If you could imagine all this pain in one blast it is about right, maybe even worse.”

Brain Cancer

Similarly, tumors in the brain are rarely painful on their own, largely because the brain itself has no pain receptor. But they can press up against the blood vessels or nerves that surround the brain and steadily build up pressure.

This often leads to persistent, possibly throbbing headaches that don’t respond to painkillers for about 50 percent of sufferers. Brain tumors, even if benign, may also cause meningitis or neuropathic pain by pressing down on the nearby spinal cord.

Ultimately, while there’s rarely one single source of cancer pain, 80 to 90 percent of it can be successfully managed with existing medications such as opioid painkillers. Unfortunately, more than 50 percent of patients with cancer pain are inadequately treated for it.