What happens after a skin biopsy, and how to read the report
After a potentially abnormal spot is found on the skin, a clinician can test that spot to find out whether it is something worrying. That test is a biopsy: a small sample of the spot is removed and sent to a laboratory, where a physician examines it under a microscope and writes a report.
The biopsy comes first, and it comes before any treatment. It is the step that answers what is this? Everything else follows from the answer. If the report shows something that needs removing, the treatment is scheduled afterward as a separate appointment, and it might be Mohs surgery, a standard excision, or something simpler.
That is worth stating plainly, because the two are easy to confuse. During Mohs surgery, tissue is also processed, stained, and read under a microscope, so the steps look almost identical from the outside. The difference is when it happens and what question it answers. A biopsy is a diagnostic test done in advance, to find out what a spot is. The microscope work during Mohs happens partway through the surgery, on tissue already known to be cancer, to check whether the edges are clear. If you are here trying to understand a Mohs appointment rather than a biopsy result, the hour-by-hour walkthrough is the article you want.
The biopsy itself takes a few minutes. Then you go home and wait, usually about a week, and that week is almost always worse than the procedure was.
Some people get a phone call. Some open a patient portal and find a pathology report sitting there, written in a language nobody taught them, sometimes before anyone has called to explain it. That last situation is common now and genuinely unpleasant, so this article is written for it: what is happening during the wait, how a report is put together, what the words mean, and which parts are more uncertain than they look.
What is actually happening while you wait
The tissue does not go straight under a microscope. It has to be turned into something a microscope can read, and that takes real time regardless of how urgently anyone wants the answer.
- Fixation. The specimen sits in preservative so the tissue stops changing.
- Processing and embedding. Water is removed and replaced with wax, so the tissue is firm enough to slice. This step usually runs overnight.
- Sectioning. The block is cut into slices a few thousandths of a millimeter thick and floated onto glass slides.
- Staining. Tissue is naturally almost colorless. Dyes are what make the structures visible.
- Reading. A pathologist examines the slides and writes the report.
- Sometimes more. Special stains, deeper levels cut from the same block, or a second opinion from another pathologist. Each of these adds days, and each of them is a sign of care rather than a sign of bad news.
If it is taking longer than expected
Most results come back in about a week. Sometimes they do not, and the wait stretches past two. You may get a call from your clinician letting you know there is a delay, which is unsettling precisely because it arrives before any answer does.
Here is what it usually means. The pathologist decided the case needed more than a routine read, so they ordered additional stains, which reveal features the standard stain does not show, or sent the material to a subspecialist who concentrates on that kind of case. Often both. If the slides have to physically travel to another laboratory, that alone adds days.
What that does and does not tell you:
- It does mean the case is more complex to interpret than a straightforward one, and that somebody wanted more information or another set of eyes before committing to an answer.
- It does not mean cancer has been found. A delay is not a preview of the result, and plenty of these come back benign.
The instinct is to read a delay as ominous. In practice it usually indicates the opposite of carelessness: the first look was not considered good enough to act on, so more was done.
How a report is built
Reports vary between labs, but nearly all of them have the same bones. Knowing which section does what tells you where to look.
| Section | What it is |
|---|---|
| Clinical history or indication | What your physician told the lab: the site, the size, what it was thought to be. Context, not findings. |
| Gross description | What the specimen looked like to the naked eye before processing. Usually a few millimeters of skin. Rarely meaningful to you. |
| Microscopic description | What the pathologist saw. Dense and technical, and not the conclusion. |
| Diagnosis | The line that matters. Often at the top, sometimes at the bottom. If you read one section, read this one. |
| Margins | Whether the cells of the lesion reach the cut edge of the sample. See the section below before interpreting it. |
| Comment or note | Where the pathologist explains reasoning, flags uncertainty, or recommends something. Often the most informative part after the diagnosis. |
| Addendum | Added later, usually after special stains or a second opinion. It may revise what came before, so an addendum supersedes the original. |
Margins, and why that line is not a verdict on its own
If your report says the margins are involved or positive, or that the lesion extends to the edge of the specimen, it is telling you something specific. On at least one slide, the cells of the lesion reached the edge of the piece of tissue that was taken. In practical terms, that means there are likely more of those cells still in your skin.
What follows from that depends entirely on what the cells turned out to be.
- If the lesion is benign, more of it remaining may require nothing further at all.
- If it is not benign, it may mean your clinician wants to take more.
Which is why this line cannot be read on its own. It describes the sample. The plan comes from combining it with the diagnosis, the location, and what your clinician saw at the visit. It is also a common finding rather than a sign that something went wrong during the procedure, because most biopsies are taken to get enough tissue to make a diagnosis rather than to remove the whole spot.
Do not draw conclusions from the margin line before you have spoken to your provider. It is one input into a decision, not the decision.
The vocabulary
Most of a pathology report is a small set of terms used precisely. Here is what they generally mean.
What kind of thing it is
| Term | What it means |
|---|---|
| Benign | Not cancer. |
| Atypical, dysplastic | Cells that are not normal and also not cancer. A middle category, and the one where careful pathologists most often disagree with each other. |
| In situ | Abnormal cells confined to the top layer of skin. They have not invaded downward. Very treatable. |
| Invasive | The abnormal cells have grown into deeper tissue. This is the word that changes the plan. |
| Carcinoma | A cancer arising from the cells that line surfaces, which includes basal cell and squamous cell carcinoma. |
How certain the pathologist is
This is the part patients most often miss, because the phrasing is subtle and it is doing real work.
| Phrasing | Confidence |
|---|---|
| Diagnostic of, consistent with | Confident. This is the answer. |
| Suggestive of, favor, most consistent with | Leaning that way, not certain. |
| Cannot exclude, atypical features, indeterminate | Genuinely uncertain. Expect further steps rather than a conclusion. |
| Recommend complete excision for definitive evaluation | The sample was not enough to settle it. This is a request, not a formality. |
Measurements and features
| Term | What it means |
|---|---|
| Breslow depth | How deep the tumor reaches, in millimeters. |
| Clark level | Which anatomic layer of skin the tumor reached, on a scale of I to V. An older way of describing the same idea. |
| Well, moderately, or poorly differentiated | How far the cells have drifted from normal. Poorly differentiated behaves less predictably. |
| Mitotic rate | How actively the cells are dividing. |
| Ulceration | The surface has broken down. |
| Perineural invasion | Tumor traveling along a nerve, which is a route beyond the visible area. |
| Lymphovascular invasion | Tumor found inside blood or lymphatic vessels. |
| Infiltrative, morpheaform, sclerosing, micronodular | Growth patterns that extend in fine strands past the visible edge. |
Several of those terms do more than describe. They change what treatment is appropriate, and the full list of which ones and why is in the article on when Mohs surgery is indicated.
What “atypical” actually means
No single word on these reports generates more worry, and it is worth being precise about it. Atypical does not mean early cancer. It means the cells are not normal and are also not malignant, which is a real and legitimate category rather than a hedge.
The practical consequences are usually modest. Depending on what was found and how it was described, the plan may be to remove a little more, to watch the site, or to do nothing further at all. What atypical almost never means is that you have cancer and nobody wants to say so.
It is also, as the next section explains, the category where pathologists most often see things differently from one another.
A pathology report is an expert interpretation, not a measurement
This section is the one I most want people to understand, and it has to be said carefully, because it is easy to hear it wrongly.
A pathology report is not a blood test. Nothing gets counted by a machine and printed. A trained physician looks at cells through a microscope and makes a judgment, and for most skin specimens that judgment is clear and reproducible: a basal cell carcinoma looks like a basal cell carcinoma.
But some categories are genuinely hard, and the difficulty has been measured rather than merely suspected.
- In a long-running quality assurance program that circulated the same slides to many dermatopathologists, overall agreement was 77 percent, with major disagreement in 7 percent of cases. Melanocytic lesions, meaning moles and things resembling them, were among the areas flagged as consistently difficult. One particular benign lesion was misread as melanoma by 40 percent of participants. [1]
- When a melanoma referral center re-examined specimens that had already been diagnosed elsewhere, the diagnoses disagreed 14.3 percent of the time. [2]
Here is what that does and does not mean.
It does not mean pathology is unreliable. The disagreement is concentrated in a specific and well-known place: the ambiguous middle ground between an unusual mole and an early melanoma. Clear-cut cases are read consistently. Anyone in the field will tell you which cases are hard, and they are the same ones the studies identify.
What it does mean is that hedged language in a report is honest rather than evasive, that a second opinion on a borderline melanocytic lesion is ordinary good practice rather than an accusation, and that “the pathologist was not sure” is sometimes the correct and complete answer. It also explains why an ambiguous result may lead to removing more tissue: when the reading is uncertain, more tissue often settles it.
Second opinions
Two things worth knowing.
First, one may already have happened. Difficult cases are routinely shown to colleagues or sent to a subspecialist before the report is finalized. If your report mentions review by another pathologist or has an addendum, that process worked as intended.
Second, asking for one is reasonable and not an insult to anyone. The situations where it makes the most sense are the ambiguous melanocytic diagnoses described above, any result that would commit you to a major operation, and any result that does not fit what your physician expected clinically. That last one matters: if the spot looked like one thing and read as another, somebody should reconcile that rather than let it stand.
The slides physically exist and can be sent elsewhere. You do not need another biopsy to get another opinion.
What to ask
- In plain language, what did this find? A one-sentence answer should exist. If it does not, that is itself informative.
- Was this a sample or a removal? It determines what the margin line means.
- How certain is this diagnosis? Reports carry confidence in their phrasing, and your physician can translate it.
- Does anything here change the treatment? Growth pattern, depth, differentiation, and nerve involvement often do.
- What happens next, and by when? Including what should prompt you to call sooner.
If you are reading this in a portal at eleven at night
Which is how a lot of people meet their pathology report, since results are often released automatically before anyone has called.
Find the diagnosis line and read that. Skip the microscopic description, which is written for other physicians and is not where the conclusion lives. If there is an addendum, it is more current than what precedes it. Then stop, because the next useful thing is a conversation, and reading the same paragraph twenty times will not produce one.
Most skin biopsies come back benign. Of the ones that do not, the majority are basal cell or squamous cell carcinomas, which are very treatable, and the earlier they are dealt with the smaller the whole business is.
The bottom line
A pathology report is a specialist writing to another specialist, which is why it reads the way it does. It was not written to be withheld from you, and it was not written to be understood by you either.
Three things carry most of the meaning: the diagnosis line, whether the words in situ or invasive appear, and how confidently the whole thing is phrased. Where the report hedges, that is usually a pathologist being honest about a genuinely difficult call rather than one hiding something.
Bring it to your appointment with the parts you did not understand marked. Working through it out loud takes a few minutes and is a much better use of the visit than pretending it all made sense.
References
- Peck M, Beer TW, Badrick T, Wood BA. The RCPA quality assurance program in dermatopathology: a retrospective review. Am J Dermatopathol. 2018;40(3):191-197. doi:10.1097/DAD.0000000000000922
- Shoo BA, Sagebiel RW, Kashani-Sabet M. Discordance in the histopathologic diagnosis of melanoma at a melanoma referral center. J Am Acad Dermatol. 2010;62(5):751-756. doi:10.1016/j.jaad.2009.09.043
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Medical content: William S. Farmer, MD · Last reviewed: July 2026
