15 possible warning signs of cancer, why they can be easy to overlook, and when persistent or unexplained symptoms should be evaluated by a doctor. Cancer can sometimes develop without obvious symptoms, especially in its early stages. When symptoms do occur, they are often nonspecific and may be caused by many conditions that are not cancer.
That is why the goal isn’t to panic over every unusual symptom. Instead, it’s to recognize persistent, unexplained, or changing symptoms and get them checked when appropriate.
1. Unexplained Weight Loss
Losing weight without intentionally changing your diet or exercise routine can have many causes, including thyroid problems, digestive disorders, infections, stress, and other illnesses.
However, unexplained or significant weight loss can sometimes occur with cancers such as pancreatic, stomach, esophageal, or lung cancer.
If you’re losing weight without trying, particularly if the loss is substantial or accompanied by other symptoms, speak with a healthcare professional.
2. Persistent Unusual Fatigue
Everyone gets tired. Lack of sleep, stress, anemia, infections, medications, and many other conditions can cause fatigue.
Cancer-related fatigue may feel different from ordinary tiredness and may persist despite adequate rest.
Persistent unexplained fatigue deserves medical evaluation, particularly when it occurs alongside weight loss, pain, bleeding, or other changes.
3. An Unexplained Lump or Swelling
A new lump under the skin, in the breast, neck, armpit, abdomen, or another area should not automatically be assumed to be cancer.
Many lumps are harmless, such as cysts or enlarged lymph nodes.
But a lump that persists, grows, becomes firm, or changes should be examined by a healthcare professional.
4. Unusual Bleeding
Unexpected bleeding can have many causes, but certain patterns should be evaluated.
Examples include:
- Blood in the stool
- Blood in the urine
- Coughing up blood
- Vomiting blood
- Unusual vaginal bleeding
- Bleeding after menopause
The cause may be something other than cancer, but unexplained bleeding should never simply be ignored.
5. Persistent Changes in Bowel Habits
A temporary change in bowel movements is common.
More concerning is a persistent change such as ongoing diarrhea, constipation, unusually narrow stools, or a change in your normal bowel pattern.
These symptoms can occur with conditions such as irritable bowel syndrome, infections, dietary changes, hemorrhoids, and colorectal cancer.
6. Persistent Changes in Urination
Changes such as frequent urination, difficulty urinating, pain while urinating, or blood in the urine can have several causes, including urinary infections and prostate problems.
However, persistent or unexplained urinary changes should be evaluated.
Blood in the urine deserves medical attention even if there is no pain.
7. A Persistent Cough or Hoarse Voice
A cough caused by a cold or respiratory infection usually improves as the illness resolves.
A cough that doesn’t go away, repeatedly returns, or is accompanied by coughing up blood, chest pain, or unexplained weight loss should be assessed.
Persistent hoarseness can also have many causes, including reflux and vocal-cord irritation, but if it continues, medical evaluation is appropriate.
8. Difficulty Swallowing
Feeling that food is getting stuck, persistent difficulty swallowing, or painful swallowing can result from reflux, inflammation, narrowing of the esophagus, and other conditions.
Occasionally, these symptoms can be associated with cancers of the throat or esophagus.
Persistent swallowing problems should therefore be investigated rather than ignored.
9. Persistent Indigestion or Abdominal Discomfort
Occasional indigestion is extremely common.
But ongoing indigestion, abdominal discomfort, persistent bloating, early fullness, or unexplained changes in appetite may warrant evaluation—especially if they are new and don’t improve.
These symptoms are not specific to cancer, so don’t assume the worst. A doctor can determine the likely cause.
10. Skin Changes or a Changing Mole
One of the most important skin warning signs is a new or changing spot or mole.
Watch for the ABCDE pattern:
- A — Asymmetry: one half doesn’t resemble the other.
- B — Border: edges are irregular or poorly defined.
- C — Color: color varies within the lesion.
- D — Diameter: larger than about 6 mm can be a warning sign, although melanomas can be smaller.
- E — Evolving: the spot changes in size, shape, color, or appearance.
A sore on the skin that doesn’t heal should also be examined.
11. Persistent Pain Without an Obvious Explanation
Pain is extremely common and usually has a non-cancerous cause.
However, persistent, unexplained, or progressively worsening pain should be evaluated, particularly when it occurs with other symptoms.
The location and character of pain can provide important clues about its cause.
12. Persistent Fever or Night Sweats
Fever is usually associated with infection, but persistent unexplained fever can occasionally occur with certain cancers.
Repeated drenching night sweats without an obvious explanation also deserve medical evaluation, especially when accompanied by unexplained weight loss, swollen lymph nodes, or prolonged fatigue.
13. Repeated or Persistent Infections
Some cancers can affect the immune system or blood-cell production, potentially making a person more susceptible to infections.
However, frequent infections can also result from many other medical conditions.
If infections are unusually frequent, severe, persistent, or difficult to treat, discuss the pattern with your doctor.
14. Persistent Swollen Lymph Nodes
Lymph nodes commonly become enlarged during infections and may take some time to return to normal.
A lymph node that continues growing, remains enlarged without an obvious infection, feels unusually firm, or is accompanied by other concerning symptoms should be assessed.
15. Changes in the Breast
Breast cancer does not always present as a lump.
Possible changes include:
- A new lump
- Changes in breast size or shape
- Skin dimpling
- Changes in the nipple
- Nipple discharge, particularly bloody discharge
- Persistent localized breast changes
- A new swelling in the armpit
Most breast changes are not cancer, but new or persistent changes should be checked.
One Important Thing to Remember
Having one of these symptoms does not mean you have cancer.
Many of the signs above are much more commonly caused by non-cancerous conditions. The reason to pay attention is that persistent or unexplained changes deserve an explanation.
Cancer can often be treated more effectively when detected early, but there is no single list of symptoms that can diagnose cancer. Screening is also important because some cancers can be found before symptoms appear.
Depending on your age, sex, family history, and risk factors, recommended screening may include tests for cancers such as breast, cervical, colorectal, and lung cancer.
When Should You See a Doctor?
Consider making an appointment if a symptom:
- Persists or keeps returning
- Is getting worse
- Has no obvious explanation
- Is accompanied by unexplained weight loss or severe fatigue
- Involves unexplained bleeding
- Produces a new or changing lump
- Represents a significant change from your normal health
Don’t wait for symptoms to become severe before seeking medical advice.
And remember: routine cancer screening is different from investigating symptoms. If you already have concerning symptoms, don’t wait for your next screening appointment—contact a healthcare professional for an appropriate evaluation.