Introduction
Oral squamous cell carcinoma, also known as mouth cancer or oral cancer, begins in the cells that line the inside of the mouth and lips. This type of cancer represents more than 90% of all oral malignancies and affects about 35,000 people in the United States each year. The disease can develop anywhere in the oral cavity, including the lips, tongue, gums, floor of the mouth, inside of the cheeks, hard palate, and the area behind the wisdom teeth.[1][2]
Understanding who should undergo diagnostic testing and when to seek medical attention is crucial for preventing this disease from progressing to dangerous stages. People who use tobacco products—whether cigarettes, cigars, pipes, or smokeless tobacco like chewing tobacco—face significantly higher risk. Those who drink alcohol heavily are also at increased risk, and the combination of heavy smoking and heavy alcohol consumption raises the risk dramatically. Over 95% of people with oral squamous cell carcinoma either smoke tobacco, drink alcohol, or both.[1][6]
Anyone experiencing persistent changes in their mouth should seek diagnostic evaluation. This includes non-healing sores, white or red patches that don’t go away, lumps or thickening in the mouth or lips, persistent pain, difficulty swallowing, or numbness. Because early lesions are rarely symptomatic, people with risk factors should undergo regular oral screening even without symptoms. Most oral cancers occur after age 50, though they can affect younger individuals as well.[1][3]
Diagnostic Methods
Physical Examination and Oral Screening
The diagnostic process for oral squamous cell carcinoma typically begins with a thorough physical examination of the oral cavity. Dentists and oral pathologists play an essential role in early detection, as they are often the first to identify suspicious lesions during routine dental examinations. The examination includes visual inspection and palpation of all areas inside the mouth, including the tongue, floor of the mouth, gums, cheeks, lips, and the roof of the mouth.[2]
During the screening, healthcare professionals look for specific changes that might indicate cancer or precancerous conditions—abnormal tissue changes that may develop into cancer if left untreated. These include areas of leukoplakia, which are flat white or gray patches in the mouth that cannot be scraped away. They also look for erythroplakia, which are red patches that may be slightly raised or flat and might bleed when scraped. A third type of concerning patch is erythroleukoplakia, which shows both red and white coloring. These patches are particularly important because they can be precancerous or already cancerous.[1][6]
The examination also identifies other warning signs such as non-healing sores or ulcers with irregular floors and margins that feel hard when touched, lumps or thickening in any part of the mouth, areas of numbness, or loose teeth without obvious cause. Healthcare providers pay special attention to the most common sites where oral cancer develops—the tongue and the floor of the mouth. As the disease progresses, lesions may appear as ulcers or masses and can invade surrounding structures, leading to tooth mobility, difficulty opening the mouth, or masses in the neck region.[2][5]
Biopsy and Histopathological Examination
When a suspicious lesion is found during physical examination, a biopsy—a procedure where a small sample of tissue is removed for examination—is the definitive way to diagnose oral squamous cell carcinoma. The biopsy allows pathologists to examine tissue specimens under a microscope for histopathological features, which are the microscopic characteristics that indicate whether cells are malignant or cancerous.[2]
The biopsy procedure can be performed in different ways depending on the size and location of the suspicious area. For smaller lesions, the entire abnormal area may be removed in what’s called an excisional biopsy. For larger areas, a small representative sample is taken through an incisional biopsy. The tissue is then sent to a laboratory where oral pathologists examine it to determine whether cancer cells are present and, if so, what type and grade of cancer it is.[8]
The histopathological examination not only confirms whether cancer is present but also provides information about the cancer’s characteristics. Pathologists look at how the cells are arranged, how abnormal they appear, and how aggressive they seem to be. This information helps doctors understand the cancer’s behavior and plan appropriate treatment. Because the clinical appearance of oral squamous cell carcinoma can resemble other common oral conditions, careful examination of biopsy specimens is essential for accurate diagnosis.[2]
Imaging Studies
Once oral cancer is diagnosed through biopsy, imaging studies help determine the extent of the disease and whether it has spread to nearby structures or distant organs. These tests create pictures of the inside of the body and are crucial for staging—determining how advanced the cancer is—which guides treatment decisions.[8]
Computed tomography (CT) scans use X-rays taken from different angles to create detailed cross-sectional images of the body. CT scans of the head and neck can show whether the cancer has spread to lymph nodes in the neck or has invaded nearby bone or other structures. This information is particularly important because oral cancer often spreads to lymph nodes on the same side of the neck as the primary tumor, though it can also affect lymph nodes on both sides or the opposite side.[1]
Magnetic resonance imaging (MRI) uses powerful magnets and radio waves to create detailed images of soft tissues. MRI is especially useful for evaluating the extent of tumor invasion into the tongue and floor of the mouth, as these areas have complex soft tissue anatomy. The images help surgeons plan the extent of surgery needed to remove the cancer completely while preserving as much normal tissue and function as possible.[8]
Positron emission tomography (PET) scans involve injecting a small amount of radioactive sugar into the bloodstream. Cancer cells, which typically use more energy than normal cells, absorb more of this radioactive sugar and appear as bright spots on the scan. PET scans are particularly useful for detecting cancer that has spread to distant parts of the body, such as the lungs, bones, or liver, which are typical locations for oral cancer metastases.[7]
Chest X-rays or CT scans of the chest are commonly performed to check whether the cancer has spread to the lungs. This is important because lung metastasis significantly affects treatment options and prognosis. These imaging studies provide a complete picture of the cancer’s extent and help the medical team develop a comprehensive treatment plan.[1]
Advanced Diagnostic Techniques
In addition to traditional diagnostic methods, healthcare providers may use advanced techniques to improve detection of malignant or premalignant oral lesions. These methods help identify cancer earlier or provide additional information about the cancer’s characteristics.[2]
Molecular biology techniques can analyze genetic changes in cancer cells. These tests look for specific genetic mutations—changes in the DNA of cells—that drive cancer development. Understanding which genes have changed can sometimes help predict how aggressive the cancer might be or whether it will respond to specific treatments. For example, testing for human papillomavirus (HPV) may be performed, as HPV infection can play a role in some oral cancers, though it is identified less often in oral cavity cancer than in cancers of the throat.[1][8]
Some diagnostic approaches use special dyes or lights to make abnormal tissue easier to see during examination. While these are not yet standard in all settings, they represent evolving tools that may help healthcare providers detect suspicious areas that might otherwise be missed during routine visual examination.[2]
Diagnostics for Clinical Trial Qualification
For patients considering participation in clinical trials—research studies testing new treatments—specific diagnostic tests are required to determine whether they qualify for enrollment. Clinical trials have strict inclusion and exclusion criteria, which are standards that determine who can participate in the study. These criteria ensure patient safety and help researchers obtain reliable results.[4]
Standard qualification testing typically includes confirmation of the diagnosis through biopsy and histopathological examination. The tissue samples must show squamous cell carcinoma, and the pathology report must document specific features of the cancer. Trials often require detailed staging information obtained through imaging studies such as CT scans, MRI, or PET scans to confirm the extent of disease.[8]
Many clinical trials also require baseline laboratory tests to assess the patient’s overall health and organ function. Blood tests check kidney and liver function, blood cell counts, and other markers that indicate whether the patient is healthy enough to tolerate experimental treatments. These tests establish a starting point that researchers can compare to results obtained during and after treatment.[4]
For trials testing targeted therapies or immunotherapies, additional molecular testing may be required. These tests look for specific biomarkers—measurable characteristics of the cancer—that indicate whether the experimental treatment is likely to work. For example, testing might identify specific proteins on the cancer cell surface or genetic changes that the experimental drug is designed to target. Patients whose cancers have these specific features are more likely to benefit from the experimental treatment.[4]
Clinical trials may also require assessment of the patient’s performance status, which is a measure of how well the patient can perform daily activities. This is typically evaluated using standardized scales that rate the patient’s ability to care for themselves, work, and carry out normal activities. Better performance status usually indicates that the patient is more likely to tolerate intensive treatments and complete the full course of the experimental protocol.[10]
