Papillary Thyroid Carcinoma: Understanding Your Pathology Report

by Jason Wasserman MD PhD FRCPC
April 20, 2026

Papillary thyroid carcinoma is the most common type of thyroid cancer, accounting for approximately 80 percent of all cases. It starts from follicular cells, the cells that normally make thyroid hormone. The thyroid is a butterfly-shaped gland at the front of the neck that helps regulate metabolism, heart rate, and body temperature.

The word “papillary” describes how many of these tumors look under the microscope. They often form tiny, finger-like projections of tissue called papillae. However, not all papillary thyroid carcinomas form obvious papillae, and several subtypes grow in different patterns.

What are the symptoms of papillary thyroid carcinoma?

Many people with papillary thyroid carcinoma have no symptoms at all, and the tumour is found by chance on imaging or during a routine neck examination. When symptoms do occur, they may include a lump or swelling in the neck, a hoarse voice, trouble swallowing, or a sense of fullness or pressure in the front of the neck. Trouble breathing or a persistent cough can develop if a larger tumour presses on nearby structures.

What causes papillary thyroid carcinoma?

The exact cause of papillary thyroid carcinoma is not fully understood. Like most cancers, it develops when thyroid cells acquire genetic changes that cause them to grow and divide in an uncontrolled way.

Known risk factors include previous exposure to radiation (especially during childhood), a personal or family history of thyroid cancer, and certain inherited conditions. Papillary thyroid carcinoma is more common in women than in men, and it often develops at a younger age than other thyroid cancers.

How is the diagnosis of papillary thyroid carcinoma made?

The diagnosis usually begins when a thyroid nodule is found during a physical exam or on an imaging test such as an ultrasound. The next step is typically a fine needle aspiration (FNA), in which a thin needle is used to remove a small sample of cells from the nodule for examination under the microscope. Under the microscope, the pathologist looks for specific changes in the nucleus (the part of the cell that contains the genetic material). These nuclear changes are very characteristic, and in most cases, an FNA is enough to confirm the diagnosis of papillary thyroid carcinoma. Some features — such as the tumour’s size, whether it has grown beyond the thyroid, and whether it has entered blood vessels — can only be assessed after the thyroid has been surgically removed and the entire tumour examined. Imaging may also be used before or after surgery to check for spread to lymph nodes in the neck or to distant parts of the body.

What does papillary thyroid carcinoma look like under the microscope?

The diagnosis of papillary thyroid carcinoma is based mainly on changes seen in the nucleus of the tumour cells. These are called the nuclear features of papillary thyroid carcinoma and include:

Enlarged nuclei. The nuclei of tumour cells are larger than those of normal thyroid cells.
Pale or clear-appearing nuclei. The genetic material inside the nucleus is pushed to the edge, making the center of the nucleus look empty.
Nuclear grooves. Fine lines can be seen running down the middle of the nuclei.
Nuclear pseudoinclusions. Small, round areas inside the nucleus that look like tiny bubbles.
Overlapping nuclei. The cells are crowded together, and the nuclei appear to pile on top of each other.

In addition to these nuclear features, many tumors form papillae (finger-like tissue projections) and contain small, round calcium deposits called psammoma bodies. Both features are very suggestive of papillary thyroid carcinoma when present.

Subtypes of papillary thyroid carcinoma

Not all papillary thyroid carcinomas behave the same way. Pathologists use the term “subtype” (sometimes called “variant”) to describe tumors that look different under the microscope and may behave differently. Most subtypes behave like the classic subtype described below. A smaller number behave more aggressively and may need more intensive treatment and follow-up.

Classic subtype

The classic subtype (also called the conventional subtype) is the most common form. The tumour cells form papillae and show all of the typical nuclear features of papillary thyroid carcinoma. The classic subtype often spreads to lymph nodes in the neck but usually has a very good outlook with treatment.

Infiltrative follicular subtype

In the infiltrative follicular subtype, the tumour cells grow as small round groups called follicles rather than papillae. Unlike some other follicular-pattern tumors, this subtype lacks a well-defined capsule (border) and grows into the surrounding thyroid tissue. Despite this, its behavior is generally similar to the classic subtype.

Oncocytic subtype

In the oncocytic subtype, the tumour cells are larger than normal and appear bright pink under the microscope because they are packed with structures called mitochondria (the energy factories of the cell). These are sometimes called Hürthle cells. The outlook for this subtype is generally similar to the classic subtype.

Tall cell subtype

The tall cell subtype is considered more aggressive. The tumour cells are at least three times as tall as they are wide. This subtype is more common in older adults, is more likely to grow beyond the thyroid, and more often spreads to lymph nodes. It is also more likely to carry a BRAF V600E mutation (see biomarkers below).

Hobnail subtype

The hobnail subtype is an aggressive form in which the tumour cells appear to hang off the surface of the papillae, with bulging nuclei and a narrow base — a shape that looks like a hobnail (a short, thick nail). This subtype is more likely to grow beyond the thyroid and to spread to lymph nodes and distant sites such as bone.

Solid/trabecular subtype

In this subtype, the tumour cells grow in solid nests or long cords rather than forming papillae. It tends to behave more aggressively than the classic subtype and carries a higher risk of spreading to distant organs such as the lungs.

Diffuse sclerosing subtype

The diffuse sclerosing subtype is seen more often in children and young adults. It usually involves both lobes of the thyroid, shows extensive scarring throughout the gland, and often spreads to lymph nodes in the neck and to the lungs. Despite being more aggressive at presentation, long-term treatment outcomes are often favorable, particularly in younger patients.

Columnar subtype

The columnar subtype is rare but behaves aggressively. The tumour is composed of tall, columnar cells whose nuclei appear layered on top of one another. It is more likely than the classic subtype to spread beyond the thyroid and to distant organs.

Biomarkers in papillary thyroid carcinoma

Biomarkers are molecular features of a tumour that can affect how it behaves and how it is treated. In papillary thyroid carcinoma, biomarker testing is usually performed on tumour tissue using techniques such as next-generation sequencing (NGS), polymerase chain reaction (PCR), or immunohistochemistry. The most important biomarkers in papillary thyroid carcinoma are described below.

BRAF V600E mutation

The BRAF gene makes a protein that helps control cell growth. A specific change called the V600E mutation keeps this protein switched on all the time, which drives tumour growth. BRAF V600E is the most common molecular change in papillary thyroid carcinoma and is especially common in the classic and tall cell subtypes.

Tumors with a BRAF V600E mutation may behave more aggressively and sometimes respond less well to radioactive iodine therapy. In advanced cases that cannot be controlled with standard treatment, targeted drugs that block BRAF (such as dabrafenib combined with trametinib) can be effective.

RAS mutations

The RAS family of genes (HRAS, KRAS, and NRAS) also makes proteins that help control cell growth. Mutations in these genes are most often found in follicular-pattern papillary thyroid carcinomas, including the infiltrative follicular subtype. RAS-mutated tumors tend to behave less aggressively than BRAF-mutated tumors, but may have a slightly higher risk of spreading through the bloodstream than through lymph nodes.

RET fusions (RET/PTC rearrangements)

A fusion occurs when part of one gene is joined to part of another, creating an abnormal protein. In papillary thyroid carcinoma, fusions involving the RET gene (often called RET/PTC rearrangements) produce a protein that sends constant growth signals to the cell. These fusions are more common in younger patients and in people with a history of radiation exposure. When the tumour cannot be controlled with standard treatment, targeted drugs that block RET (such as selpercatinib and pralsetinib) can be very effective.

Tumour size

After the thyroid is removed, the tumour is measured in three dimensions, and the largest measurement is reported. Tumour size is important because larger tumors are more likely to spread to lymph nodes or beyond the thyroid, and it is one of the main pieces of information used to decide the pathologic tumour stage (pT).

Multifocal tumours

It is not unusual for more than one papillary thyroid carcinoma to be found in the same thyroid gland. When this happens, the tumour is described as multifocal. Each tumour is measured separately, and the largest tumour is used to determine the tumour stage. The presence of multiple tumors can still be important for planning follow-up, even if each individual tumour is small.

Extrathyroidal extension

Extrathyroidal extension means the cancer has grown beyond the thyroid gland into the surrounding tissue. Pathologists describe two types:

Microscopic extrathyroidal extension. The cancer has spread just beyond the thyroid and can only be seen under the microscope.
Gross (macroscopic) extrathyroidal extension. The cancer has clearly grown into nearby structures such as the neck muscles, voice box (larynx), windpipe (trachea), food pipe (esophagus), or major blood vessels. This type is visible during surgery or on imaging.

Gross extrathyroidal extension is associated with a higher stage, a higher risk of recurrence, and more intensive treatment.

Vascular invasion

Vascular invasion (sometimes called angioinvasion) means that tumour cells have entered blood vessels outside the main tumour. Once tumour cells reach the bloodstream, they can travel to distant parts of the body, such as the lungs or bones. The presence of vascular invasion is a sign of more aggressive disease and may influence both treatment and follow-up.

Lymphatic invasion

Lymphatic invasion means that tumour cells have entered lymphatic channels, the tiny vessels that carry a fluid called lymph toward lymph nodes. Papillary thyroid carcinoma often spreads in this way to the lymph nodes in the neck. Lymphatic invasion raises the chance that nearby lymph nodes contain cancer, although, particularly in younger patients, it does not always have a major impact on long-term outcome.

Margins

Margins are the edges of the tissue removed during surgery. The pathologist examines these edges to see whether any cancer cells reach the cut surface.

Negative margin. No cancer cells are seen at the edge. This suggests that the tumour was completely removed.
Positive margin. Cancer cells are seen at the edge. This means some tumour may remain in the body, and additional treatment may be recommended.

The distance between the tumour and the nearest margin is sometimes measured, because a very close margin may also increase the risk of local recurrence.

Lymph nodes

Papillary thyroid carcinoma frequently spreads to lymph nodes in the neck. Lymph nodes are small immune organs that filter lymph fluid. Tumour cells can travel from the thyroid through lymphatic channels to reach them, and nodes closest to the tumour are usually affected first.

Neck dissection

A neck dissection is a surgical procedure in which lymph nodes are removed from specific regions of the neck, called levels 1 through 5. Nodes on the same side of the neck as the tumour are called ipsilateral (same side), while those on the opposite side are called contralateral (opposite side).

How lymph nodes are described in the report

If lymph nodes are removed, the pathologist will report:

The total number of lymph nodes examined.
The number of lymph nodes that contain cancer cells. These are called positive nodes.
The size of the largest deposit of cancer cells within a lymph node.
Whether extranodal extension is present. This means cancer cells have grown beyond the outer edge (capsule) of the lymph node into the surrounding tissue.

This information is used to determine the pathologic nodal stage (pN) and to help decide whether additional treatments such as radioactive iodine or radiation are needed.

Pathologic stage (pTNM)

The pathologic stage for papillary thyroid carcinoma is based on the size and extent of the tumour (pT), whether cancer is found in nearby lymph nodes (pN), and whether it has spread to distant parts of the body (pM). Most pathology reports include details for pT and pN.

Tumour stage (pT)

T1: Tumour 2 cm or smaller and still within the thyroid.
- T1a: Tumour 1 cm or smaller.
- T1b: Tumour larger than 1 cm but not larger than 2 cm.
T2: Tumour larger than 2 cm but not larger than 4 cm and still within the thyroid.
T3: Tumour larger than 4 cm or with early growth into the muscles around the thyroid.
- T3a: Tumour larger than 4 cm but still within the thyroid.
- T3b: Tumour of any size with gross extrathyroidal extension into the strap muscles (the muscles just in front of the thyroid).
T4: Tumour with more extensive growth outside the thyroid.
- T4a: Tumour growing into the soft tissues under the skin, voice box, windpipe, food pipe, or nearby nerves.
- T4b: Tumour growing into the tissue at the front of the spine or surrounding major blood vessels in the neck or chest.

Nodal stage (pN)

N0: No cancer found in nearby lymph nodes.
N1: Cancer found in nearby lymph nodes.
- N1a: Cancer in lymph nodes in the central part of the neck, around the thyroid.
- N1b: Cancer in lymph nodes on the side of the neck or in the upper chest.

What happens after the diagnosis?

After the diagnosis has been confirmed, your healthcare team will review your pathology report, imaging studies, and thyroid blood tests to plan treatment. This team may include an endocrinologist, a thyroid surgeon, a nuclear medicine specialist, a radiation oncologist, and a medical oncologist.

Most patients are treated with surgery to remove either part of the thyroid (lobectomy) or the entire thyroid (total thyroidectomy). Depending on the tumour size, subtype, extent of disease, and biomarker results, additional treatments may include radioactive iodine, thyroid hormone suppression therapy, external beam radiation, or, in rare advanced cases, targeted drug therapy.

After treatment, regular follow-up is needed to watch for any signs that the cancer has returned. This usually includes blood tests (including thyroglobulin in most cases), neck ultrasound or other imaging, and clinical examinations. Most patients who have had a total thyroidectomy will need to take thyroid hormone replacement for the rest of their lives.

Questions to ask your doctor

What subtype of papillary thyroid carcinoma do I have?
How large was the tumour, and was there more than one tumour in the thyroid?
Did the cancer grow beyond the thyroid (extrathyroidal extension)?
Was vascular or lymphatic invasion seen?
Were the surgical margins negative?
Were any lymph nodes involved, and was extranodal extension present?
What is my pathologic stage (pT and pN)?
Were any biomarkers, such as BRAF, RAS, or RET fusions, tested, and do they change my treatment?
Will I need radioactive iodine therapy?
How will my thyroid hormone levels be monitored after surgery?
How often will I need follow-up visits, blood tests, and imaging?