The study of disease itself — and the microscope work behind nearly every cancer diagnosis on earth.
Not one organ, not one treatment — the mechanisms. Pathology asks four questions about any illness: what causes it (etiology), how it develops (pathogenesis), what it does to cells and tissues (morphology), and what that means for the patient.
It's the bridge between the basic science of the lab and the decisions made at the bedside. Almost every cancer diagnosis starts with a pathologist looking at tissue.
Normal lung is mostly air. The alveoli — the tiny sacs where oxygen crosses into blood — show up as open white spaces framed by delicate pink walls just one or two cells thick. Everything is spacious, regular, and repeating.
Hold this image in your head. In a few slides you'll see what happens when cancer fills those spaces in — and the contrast is the whole point.
Pathologists rarely meet the patient — but their report drives what happens next. When a surgeon removes a tumor, the pathologist determines whether it's cancer, what type, how aggressive, and whether it was fully removed. Oncologists can't choose a therapy until that report lands.
Benign or malignant? And what exactly is it?
Grade, stage, margins, and molecular markers that guide therapy.
The report becomes the roadmap for the whole care team.
Diagnosis by examining the structure of tissues and cells — what the disease looks like under the microscope and to the naked eye. The world of biopsies, tumors, and slides.
Diagnosis through laboratory analysis of body fluids — blood, urine, marrow. Measuring, counting, and detecting rather than looking. Also called laboratory medicine.
Molecular & computational pathology cuts across both — and it's where cancer research is moving fastest.
The largest subfield. Examines tissue removed in surgery or biopsy — the engine of cancer diagnosis.
Microscopic study of stained tissue sections. The core skill you'll practice in the lab.
Diagnosis from individual cells — Pap smears, fine-needle aspirates. Faster, less invasive.
Post-mortem exam to establish cause of death and advance medical understanding.
Autopsy in a legal context — trauma, toxicology, time and manner of death.
Specialized study of nervous-system tissue — brain tumors, neurodegeneration.
Chemical analysis of blood and fluids — glucose, enzymes, hormones, tumor markers.
Diseases of blood and marrow — leukemias, lymphomas, anemias.
Identifying bacteria, viruses, fungi, parasites — and what will treat them.
Blood typing, cross-matching, and the safe management of the blood supply.
Disorders of the immune system — autoimmunity, allergy, immunodeficiency.
Detecting disease at the level of DNA, RNA, and protein. Coming up next.
Modern diagnosis isn't just "what does it look like" — it's "what is it made of, genetically." Immunohistochemistry (IHC) stains for specific proteins. Sequencing reads the tumor's mutations. And increasingly, algorithms read the slides.
Antibodies tag a target protein so it shows up in color — is the tumor expressing this marker?
Sequencing finds actionable mutations (EGFR, KRAS, ALK); ML models grade whole-slide images. The thread tying pathology to everything CRS docks, screens, and models.
Every slide you'll look at in the lab traveled this exact path. When you look down the microscope, you're seeing the end of a nine-step journey.
Sections are cut to about 4–5 micrometers — so thin that light passes through and you see a single flat layer of cells rather than a confusing stack. The paraffin block makes it possible: wax turns soft, wet tissue into something firm enough to shave cleanly.
Fixation matters just as much. The moment tissue leaves the body it begins to break down. Formalin cross-links the proteins and freezes the architecture — so what you see is the disease, not decay.
Raw tissue is nearly colorless. The H&E stain — hematoxylin and eosin — is the most-used stain in all of medicine, and it's what gives histology its signature look.
Train your eye on these five features — they're what separates a benign slide from a malignant one, and what you'll hunt for in the lab.
How far the cells have drifted from normal. Well-differentiated still looks almost like the original tissue; poorly differentiated is barely recognizable. Higher grade usually means more aggressive.
How much territory the cancer has taken. Size of the tumor (T), lymph node involvement (N), and whether it has metastasized to distant organs (M). The TNM system.
A tumor can be high-grade but early-stage, or low-grade but widespread. You need both numbers to know what you're dealing with.
Two slides in the lab aren't teaching samples — they come from an actual patient at MD Anderson Cancer Center with late-stage lung adenocarcinoma that has metastasized. Compare this against the normal lung from slide 04.
Cancer of glandular, secretory cells — the most common lung cancer type.
Arises from epithelial (lining) cells. Most human cancers are carcinomas.
Broken free and seeded a distant organ. This is what makes cancer lethal.
Irregular glands where they don't belong; crowded dark nuclei; lost architecture.
Not every diagnosis requires cutting tissue. In cytopathology, loose cells — scraped, brushed, or drawn out with a fine needle — are spread on a slide directly. It's faster and far less invasive, the approach behind the Pap smear and many first-pass cancer checks.
The trade-off: you see cells in isolation, losing the tissue architecture that histology preserves. Often it's the first look that decides whether a biopsy is needed.
This past summer I trained at MD Anderson Cancer Center through the DPLM ONCORE Youth Summer Program, in the Department of Pathology & Laboratory Medicine. The project turned our own learning into the experiment: could pathology-naïve high school students, after hands-on teaching, reliably score FOLR1 immunohistochemistry — the companion biomarker that decides mirvetuximab eligibility in platinum-resistant high-grade ovarian / fallopian-tube / peritoneal cancer?
This deck was the warm-up. In the lab, you put it to work.
The same rigor you brought to the microscope, aimed at the page. How to search PubMed like a researcher, read a paper without drowning, and tell good science from bad.
Before you dock a molecule, run a screen, or design a study, you have to know what's already been done — what's settled, what's contested, and where the gap is that your work could fill. A literature review is how you find the edge of human knowledge before trying to push it.
Learn the field's language, key players, and landmark papers fast.
Don't spend months on a question already answered in 2019.
The unanswered question is your research opportunity.
A broad, expert summary of a topic. Flexible, readable, good for orientation — but the author chooses what to include, so it can carry bias. This is what most student "lit reviews" actually are.
A reproducible method: a pre-defined question, an explicit search protocol, and strict inclusion/exclusion criteria applied to every paper found. Meta-analyses pool their numbers. The gold standard — and much more work.
Start narrative to learn a field. Go systematic when you need an answer you can defend.
"Lung cancer treatment" returns half a million papers. Narrow it until it's answerable. In clinical research the PICO frame helps structure it:
Who? e.g. EGFR-mutant NSCLC patients
What? e.g. osimertinib
Versus? e.g. first-gen TKIs
Measuring? e.g. progression-free survival
Those four pieces become your search terms. The question writes the query.
PubMed indexes 37+ million biomedical citations from MEDLINE and beyond, maintained by the NIH's National Library of Medicine. Searching it like a search engine wastes its real power. The payoff is in structured search: MeSH terms, boolean logic, and field tags.
Free to search. Many results link to free full text via PubMed Central (PMC).
Authors might write "heart attack," "myocardial infarction," or "MI." MeSH — Medical Subject Headings — is a standardized vocabulary where all of those map to a single official term. Search the MeSH term and you catch every paper on the concept, no matter the wording.
MeSH also has a hierarchy — searching a broad term can automatically include its narrower children ("explode").
Free full text · publication date · article type (Review, RCT, Meta-Analysis) · species. One click each — huge time savers. Use "Review" to find existing lit reviews that hand you a reading list.
Google Scholar — widest net, catches preprints & citations. Connected Papers — visual map of what cites what. Scopus / Web of Science — citation tracking. bioRxiv/medRxiv — preprints (unreviewed).
Citation chasing: found one great paper? Read its references (backward) and see what cited it (forward). Often faster than any search.
A good search returns dozens to hundreds of hits. Triage in layers — spend seconds before you spend hours.
Decide your inclusion/exclusion criteria up front (years, study type, language) so you're not deciding case-by-case and drifting.
Never read a paper front to back on the first go. Make three increasingly deep passes — most papers get cut after pass one.
Title, abstract, figures, conclusion. What did they do and find? Decide if it's worth more time.
Read the body, skim the math. Grasp the methods and whether the evidence supports the claims.
Reconstruct it. Could you reproduce it? Where would it break? For papers central to your work.
Read figures first. In a good paper the figures tell the whole story — often faster and more honestly than the prose.
Peer review is a filter, not a guarantee. Read with these questions live — the same critical eye behind CRS's meta-research work on reporting quality.
Zotero (free, excellent) grabs citations in one click, stores PDFs, and generates your bibliography in any style. Alternatives: Mendeley, EndNote. Set this up before paper #5, not after #50.
A simple table: one row per paper, columns for question, method, sample, key finding, limitations. Fill it as you read. When it's done, your review almost writes itself — you read across rows, not down.
Capture the citation the moment you decide to keep a paper. Re-finding a lost source is the single biggest time sink in any review.
A review isn't a list of summaries ("Smith found X. Jones found Y."). It's an argument organized by theme: here's what the field agrees on, here's where it conflicts, here's the gap — and here's where my work fits.
Organize around themes and debates, not one-paper-at-a-time.
Every claim that isn't yours gets a citation. Paraphrase; never copy. Quote rarely.
End by naming the open question your research will take on.
On AI tools: fine for finding and summarizing — never trust a citation you haven't opened yourself. Models invent plausible-looking references. Verify every one.
You can now trace a specimen from patient to microscope — and a research question from a vague idea to a defensible review. Next up: the pathology lab, and your own literature search.
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