Roughly 70% of all healthcare decisions depend on laboratory test results, according to the CDC. Pathologists are the physicians responsible for producing, interpreting, and ensuring the accuracy of those results. While most patients never meet their pathologist face to face, nearly every diagnosis, treatment plan, and surgical decision passes through one.
What Pathologists Actually Do
Pathology splits into two broad branches. Anatomic pathologists examine cells and tissues under a microscope, reading biopsies, Pap smears, and surgical specimens to determine whether something is cancerous, infected, or otherwise abnormal. Clinical pathologists oversee the analysis of blood, urine, and other body fluids, covering everything from cholesterol panels to blood typing before a transfusion. Many pathologists are trained in both.
In practice, this means a pathologist is involved nearly every time your doctor orders a test. When a dermatologist shaves off a suspicious mole, a pathologist examines the tissue and reports whether it’s benign or malignant. When your blood work comes back showing abnormal white cell counts, a pathologist may review a blood smear to check for signs of leukemia or infection. They don’t just run the machines. They interpret the results, flag the unusual findings, and communicate directly with your treating physician about what those results mean for your care.
Guiding Cancer Treatment Decisions
Cancer care is one of the clearest examples of why pathologists matter. A pathologist determines the type of cancer, its grade (how aggressive it looks under the microscope), and whether it has spread to nearby lymph nodes or tissue margins. These findings directly shape whether a patient needs chemotherapy, radiation, more surgery, or close monitoring alone.
Pathologists sit on multidisciplinary tumor boards alongside surgeons, oncologists, and radiologists. These meetings are required by accreditation bodies like the American College of Surgeons. After the pathologist shares findings, the team discusses specific questions: Should a lymph node be removed? Does this patient need additional chemotherapy? Data from Kaiser Permanente found that tumor board review of pathology results led to cancer being up-staged in about 15% of patients, and 6% of patients had their plan changed from observation to chemotherapy. In other words, the pathologist’s assessment directly altered the course of treatment for a meaningful number of people.
When a second pathologist reviews a case, about 1% of cases show a major disagreement significant enough to change the patient’s treatment plan. That may sound small, but across thousands of cancer diagnoses each year, it represents real people whose care would have gone in the wrong direction without that additional review.
Real-Time Decisions During Surgery
One of the most time-sensitive roles a pathologist plays happens while a patient is still on the operating table. During a procedure called a frozen section, a surgeon removes tissue and sends it to the pathology lab. Within about 20 to 30 minutes, the pathologist freezes the sample, slices it thin, examines it under a microscope, and calls the surgeon with a result.
That phone call can change the entire surgery. If a biopsy comes back malignant, the surgeon may need to widen the area of removal. If the edges of a tumor specimen still contain cancer cells, the surgeon goes back and cuts further. If a lymph node shows signs of spread, the surgical plan expands. Without frozen sections, many patients would need a second surgery days or weeks later, adding physical stress, financial cost, and time under anesthesia. The pathologist’s rapid assessment while the patient is still in the operating room helps prevent that.
Matching Patients to Targeted Therapies
Modern cancer treatment increasingly depends on molecular pathology, a subspecialty focused on identifying specific genetic changes in a patient’s tumor. Certain mutations drive cancer growth, and drugs now exist that target those exact mutations. A pathologist who finds a particular genetic alteration in a lung tumor, for example, can identify whether the patient is eligible for a targeted drug rather than standard chemotherapy.
This approach has transformed treatment for several cancers. Genetic testing now routinely guides therapy decisions in non-small cell lung cancer, colorectal cancer, breast cancer, and others. Some of these genetic drivers appear across multiple cancer types, which has led to treatments approved based on the mutation itself rather than where the cancer started in the body. The pathologist’s molecular report is the entry point for all of it. Without that analysis, oncologists would be choosing treatments based on far less precise information, and patients who could benefit from targeted drugs might never receive them.
Tracking Infectious Disease Outbreaks
Pathologists play a critical role in identifying new and emerging infections. The CDC’s Infectious Diseases Pathology Branch is the primary unit responsible for investigating infectious diseases of unknown cause. Their team of pathologists, molecular biologists, and microbiologists can identify hundreds of different infectious agents in body tissues using advanced laboratory techniques.
During an outbreak, pathologists help confirm the cause of disease by examining tissue samples. This is especially important when standard tests come back negative or inconclusive, which is common with new or emerging pathogens. When a virus or bacterium hasn’t been seen before, pathologic examination of affected tissues can point investigators in the right direction. Tissue-based methods also feed into disease surveillance systems that monitor for early cases and help control outbreaks before they spread widely.
Ensuring Lab Accuracy and Patient Safety
Beyond interpreting individual cases, pathologists are responsible for the overall quality of a hospital’s laboratory. They oversee equipment, validate testing methods, and ensure that every result leaving the lab is accurate. As the College of American Pathologists puts it, pathologists are responsible for “the diagnostic accuracy of every test.” A single error in a blood type, a mislabeled biopsy, or a false-negative cancer screen can have serious consequences. The systems pathologists put in place to catch and prevent those errors protect patients in ways that are invisible but essential.
Learning From Autopsies
Autopsies remain one of pathology’s most important contributions to medicine, and not just for legal purposes. Clinical autopsies compare what doctors believed was happening during a patient’s life with what the tissue evidence actually shows after death. In one retrospective study, only about 55% of cases showed complete agreement between the clinical diagnosis and the autopsy findings. Roughly 18% of cases revealed a substantially different diagnosis than what clinicians had identified. These discoveries don’t just explain what happened to one patient. They reveal patterns that improve care for future patients and deepen the medical understanding of how diseases interact.
AI and the Evolving Role
Artificial intelligence is beginning to reshape how pathologists work, though it supplements rather than replaces them. In one study, AI algorithms identified breast cancer spread to lymph nodes with 99% accuracy, compared to 81% for pathologists working alone. Similar results have been seen in colon cancer, head and neck cancer, and melanoma. AI tools can also speed up workflow by quickly flagging areas of interest on tissue slides and prioritizing urgent cases.
These tools are best understood as a powerful second set of eyes. They reduce turnaround times and catch findings a human reviewer might miss on a busy day. But interpreting results in the full context of a patient’s history, communicating nuanced findings to a surgical team, and making judgment calls about ambiguous tissue still require a trained pathologist. The technology makes pathologists more efficient and more accurate, which ultimately benefits the patients whose diagnoses depend on their work.