How Is Cancer Diagnosed?

Nearly all diseases are progressive, worsening over time, but no condition intensifies as aggressively as cancer. Detecting cancer early is essential for ensuring that patients receive effective treatment. Unfortunately, it’s also notoriously difficult.

How Doctors Detect Cancer

Making a cancer diagnosisFor most patients, the difference between an early diagnosis and one that is delayed has devastating consequences. Even under the best circumstances, the likelihood of surviving an advanced cancer is low. Beyond troubling survival rates, late-stage malignancies require treatments so debilitating that many people wonder if therapy is even worth it.

It’s clear that receiving an accurate diagnosis is critical. But how to catch malignant tumors before they spread has troubled physicians for centuries, and it can still be a difficult task.

Differential Diagnosis

In order to deal with the inherent complications of detecting cancer, medical professionals have developed a “standard of care” over the years. While this standard changes from doctor to doctor, and patient to patient, every proper diagnosis is based on a process known as “differential diagnosis.”

In theory, it’s a simple technique:

  1. create a complete list of a patient’s symptoms and any lab test results available
  2. create a second list of all the conditions that could possibly cause those symptoms
  3. rank the list of conditions logically, either in terms of probability or severity
  4. go through the list, performing new tests to rule out conditions the patient doesn’t actually have
  5. once every other condition is eliminated, the one that remains is the correct diagnosis

But in practice, diagnosis is a little messier.

1. Patients Often Report Symptoms First

The vast majority of cancers are suspected initially, rather than diagnosed from the outset. Most accurate diagnoses begin when a patient notices a troubling symptom, and then asks their doctor about it.

Few people, however, are aware of every potential cancer symptom. In fact, some studies (like this one conducted in Hong Kong) suggest that people at a greater risk for specific cancers know less about those risks than people at lower risks.

Obviously, physicians have to be even more vigilant than their patients. But compounding the problem, some early tumors cause no symptoms at all, which makes routine screenings and blood tests so important.

Watch For Potential Signs Of Early Cancer:

  • Lumps or unusual masses
  • A cough that won’t go away
  • Frequent fevers
  • Poor digestion
  • Loss of appetite
  • Nausea and vomiting
  • Chronic headaches
  • Sores that won’t heal
  • Unexplained weight loss
  • Chronic fatigue

There’s another serious problem with relying on signs and symptoms alone: any number of conditions could be causing them. In fact, “cancer […] can cause almost any sign or symptom,” according to the American Cancer Society.

Signs & Symptoms: Can We Trust Red Flags Alone?

Most types of malignancy present “nonspecific” symptoms, especially in their early stages. These could be the warning signals of a cancer, but they can also be the result of benign medical conditions. Doctors who rely too heavily on signs and symptoms risk misdiagnosing their patients.

Signs and symptoms are actually different. A sign can be seen by someone else, like your doctor, while a symptom is usually internal, and only noticed by a patient.

The difficulties of interpreting symptoms, or even noticing them in the first place, has given rise to numerous preventive screenings.

2. Routine Screenings Can Highlight Symptomless Cancers

Instead of waiting for confusing signs to develop of their own accord, doctors now try to “draw them out” proactively.

For four, particularly dangerous, cancers, the US Centers for Disease Control & Prevention recommends routine screening tests:

Breast cancer

Mammograms, essentially x-ray images of the breast, are our gold standard for identifying cancerous masses before they become deadly.

The CDC recommends receiving a mammogram at least once every two years for all women between the ages of 50 and 74.

Colon cancer

Cancers of the intestine nearly always develop from benign polyps in the colon or rectum. Since these growths don’t usually cause any symptoms, and can’t be seen with the naked eye, physicians have to perform colonoscopies, using thin camera-equipped tubes to inspect the inside of a patient’s colon.

The CDC recommends beginning regular colorectal cancer screening at the age of 50 and continuing until you’re 75.

Cervical cancer

To catch the precursors to cervical cancer, the CDC recommends all women between the ages of 21 and 65 get regular Pap tests. After a small sample of cells is collected from the cervix, lab tests can check for abnormalities in growth.

A separate test checks the same cells for traces of human papillomavirus virus (HPV), which can cause cervical cells to become malignant.

Lung Cancer 

Currently, pre-emptive screening for lung cancer is only recommended for patients at an increased risk of developing the disease. Patients with a history of heavy smoking, who still smoke or quit within the last 15 years and are between 55 and 80 should get yearly screenings, according to the CDC.

Essentially, the test is a very powerful x-ray of the lungs, one that uses low doses of radiation to increase image detail.

Screening tests look for malignancies when a patient doesn’t have any symptoms. Diagnostic tests are used to figure out what’s causing a patient’s symptoms.

Screenings are often available at low or no-cost through various federal and state programs.

3. Lab & Imaging Tests Provide More Evidence

Once the presence of a cancer is suspected, doctors will begin to gather more evidence. Remember, they’ve developed a long list of conditions that could be causing a patient’s symptoms. Now they’ll collect more data to rule out incorrect diagnoses and near the truth.

Cancer Blood Tests

Some cancers cause changes in body chemistry, forcing organs to produce more or less of a chemical than usual. Cancer cells themselves manufacture odd chemicals sometimes. These “tumor markers” can be detected in a patient’s blood, as well as their urine.

Blood tests can detect these abnormalities, but like symptoms, alterations in body chemistry are often “nonspecific.” Tumor markers can be produced in the presence of benign growths, too. In fact, the British Medical Journal has found that blood tests looking specifically for tumor markers “have a limited role, if any” in the diagnosis of cancers. Their value seems to lie more in staging a malignancy than detecting one in the first place.

Other types of blood test are more conclusive, but can only detect specific kinds of cancer. Unsurprisingly, blood cancers can sometimes be diagnosed based on blood tests, but usually a biopsy of bone marrow is required to confirm the diagnosis.

Imaging Tests For Cancer

To get a more accurate, and more literal, picture of a possible cancer, physicians turn to imaging procedures. Actually looking at the inside of a patient’s body can provide more direct evidence of malignancy than “indirect” signals like symptoms or lab tests, but it’s not conclusive, either.

MRI scan to diagnose cancer

An MRI scanner at work.

Here are a few of the imaging methods physicians can use to produce detailed images of internal organs. Each one relies on a different form of energy to create its visual results.

Computed tomography (CT) scan

CT scanners quickly spin a narrow band of x-rays, very low doses of radiation, around a patient’s body.

Each rotation creates a new image and, as patients are slowly pushed through the machines, these “slices” (like the rings in a tree trunk) can be stacked together by a computer to create a 3D image of their internal organs.


Aimed at specific internal structures, ultrasound sends high-frequency sound beams shooting into the body. The beams bounce off internal organs and a computer interprets the angles at which they ricochet, ultimately creating a picture.

Magnetic resonance imaging (MRI)

MRI uses powerful magnets to affect the structure of atoms in the body.

At the center of each atom is a smaller particle, a proton, which is very sensitive to magnetic fields. By turning the magnet on and off quickly, an MRI scanner forces the atoms to align in a certain way, then come out of alignment. By interpreting these minute changes in position, a computer develops a detailed image.

Positron emission tomography (PET) scan

First, patients are injected with a small amount of “tracer,” a radioactive material that travels through the bloodstream and gathers in body tissues.

Organs that use a lot of energy absorb more of the tracer than low energy organs; cancer cells, which use even more energy, absorb the most. A machine reads where the radioactive material has been drawn to identify potential malignancies.

“Tomography” refers to the way some imaging tests create cross-section images that can be added together to get a full picture.

We’re not done yet, though. Imaging tests can tell us where tumors where, and a lot about their size and shape, but lots of tumors are perfectly benign. To figure out whether an abnormal lump of cells is malignant, whether it will continue to grow without dying, we need to investigate it further.

4. Biopsies: The Gold Standard Of Cancer Diagnosis

That’s what a biopsy does. In this procedure, doctors actually remove a sample of the tumor for investigation. Usually, biopsy samples are sent off to a laboratory and scrutinized by professionals called pathologists.

Pathologists look for things like:

  • abnormalities in the size and shape of cells
  • abnormalities in the size and shape of cell nuclei
  • changes in how cells are arranged

Doctors can also change the samples in specific ways to learn more about the cells. “Staining” is a technique in which pathologists introduce various chemical dyes to the sample. These dyes are attracted to substances produced by certain types of cancer cells, and change their color.

Every reputable medical authority agrees on one thing: biopsy is the only way to truly know whether cells are malignant or benign.
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