Cribriform Morular Thyroid Carcinoma: Understanding Your Pathology Report

by Jason Wasserman MD PhD FRCPC
April 20, 2026

Cribriform morular thyroid carcinoma (CMTC) is a rare type of thyroid cancer with a distinctive appearance under the microscope and an important link to an inherited condition called familial adenomatous polyposis (FAP). The thyroid is a butterfly-shaped gland at the front of the neck that helps regulate metabolism. CMTC was once grouped with papillary thyroid carcinoma as the “cribriform-morular variant,” but as of the 2022 World Health Organization classification, it is recognized as a separate tumor type.

About 90 percent of patients with CMTC are women under the age of 40. Approximately 30 to 40 percent of cases occur in people who have FAP, which is why identifying CMTC has important implications not only for the patient but also for their family members.

What are the symptoms of cribriform morular thyroid carcinoma?

Like other thyroid cancers, CMTC often does not cause symptoms in the early stages and is typically detected when a thyroid nodule is felt on physical exam or seen on imaging. When symptoms do develop, they may include:

A lump or swelling in the front of the neck.
Difficulty swallowing or breathing.
Hoarseness or other changes in the voice.

Because many patients with CMTC have FAP, some are first diagnosed with CMTC after a routine thyroid ultrasound performed as part of FAP surveillance, before any neck symptoms develop.

What causes cribriform morular thyroid carcinoma?

Changes in a cell signaling network cause CMTC, also known as the WNT/β-catenin pathway. In healthy cells, β-catenin (beta-catenin) is a protein located at the cell membrane, where it helps cells stick to one another. The amount of free β-catenin inside the cell is normally kept low by another protein called APC, which acts as a switch turning off the growth signal. When either APC or β-catenin is damaged, β-catenin builds up and moves into the nucleus, where it turns on genes that drive uncontrolled cell growth.

CMTC develops through one of two pathways:

Inherited APC mutations (FAP-associated CMTC). People born with a mutation in the APC gene have a condition called familial adenomatous polyposis (FAP). FAP causes hundreds of polyps to develop in the colon and a near-certain risk of colon cancer without treatment. It also increases the risk of several other tumors, including CMTC. About 30 to 40 percent of CMTC cases occur in people with FAP.
Somatic CTNNB1 mutations (sporadic CMTC). In the remaining cases, CMTC develops on its own, without a known inherited cause. These sporadic tumors most often carry a mutation in the CTNNB1 gene (which makes the β-catenin protein). The mutation is limited to the tumor cells and is not inherited or passed on to children.

Whether the underlying cause is an APC or CTNNB1 mutation, the result is the same: β-catenin accumulates in the nucleus and drives tumor growth.

How is the diagnosis of cribriform morular thyroid carcinoma made?

The diagnosis usually begins when a thyroid nodule is detected during a physical exam, on imaging tests such as ultrasound, or during routine thyroid screening in a patient with known FAP. A fine needle aspiration (FNA) biopsy is usually performed next, in which a thin needle is used to remove a small sample of cells from the nodule. Under the microscope, CMTC shows several distinctive growth patterns described in the next section, and the diagnosis can often be suggested on FNA when a pathologist experienced with this tumor recognizes the characteristic features. However, the final diagnosis is usually confirmed after surgery, when the whole tumor can be examined. Immunohistochemistry is a laboratory test that uses antibodies to detect specific proteins in the tumor cells; in CMTC, the tumor cells show a very characteristic staining pattern: abnormal nuclear staining for β-catenin (normally found at the cell membrane), positive staining for pan-cytokeratins and TTF-1, and negative or only weak staining for thyroglobulin and PAX8. The nuclear β-catenin staining pattern is considered the most important feature and essentially confirms the diagnosis. Imaging such as CT or additional ultrasound is often used to check for spread to lymph nodes in the neck or, uncommonly, to distant parts of the body.

What does cribriform morular thyroid carcinoma look like under the microscope?

Under the microscope, CMTC has a distinctive appearance that combines several different growth patterns. The two that give the tumor its name are:

Cribriform pattern. The tumor cells form groups with many small holes running through them, giving a Swiss cheese-like appearance. (“Cribriform” means sieve-like.)
Morular bodies. Small, round clusters of elongated or spindle-shaped tumor cells that resemble squamous cells (flat cells similar to those found in the skin). These small clusters are called “morules” after the Latin word for a small mulberry.

Other growth patterns are also commonly seen in the same tumor, including solid, follicular, and papillary (finger-like) patterns. An important feature that distinguishes CMTC from most other thyroid tumors is that the tumor cells do not produce colloid. This thick, pink, gel-like material normally fills thyroid follicles and stores thyroid hormone. The absence of colloid is one of the clues pathologists use to recognize this tumor.

Biomarkers and genetic testing in cribriform morular thyroid carcinoma

CMTC is defined at the molecular level by activation of the WNT/β-catenin pathway, and biomarker testing plays a central role in both confirming the diagnosis and guiding genetic counseling.

β-catenin immunohistochemistry

In normal thyroid cells, β-catenin is found at the cell membrane. In CMTC, β-catenin translocates to the nucleus, and this shift can be detected as abnormal nuclear staining on immunohistochemistry. Nuclear β-catenin staining is considered the most characteristic feature of CMTC and, when combined with the microscopic appearance, essentially confirms the diagnosis.

APC and CTNNB1 mutation testing

Molecular testing, such as next-generation sequencing (NGS), is used to identify the specific genetic cause of the tumor. Two types of results are possible:

APC mutation. A mutation in the APC gene may be a germline (inherited) mutation, meaning it was present at birth and is present in every cell in the body, including the blood. This type of mutation causes FAP. A blood test is usually needed to confirm whether the APC mutation is germline, and, if so, first-degree relatives (parents, siblings, children) should be offered genetic testing.
CTNNB1 mutation. A mutation in the CTNNB1 gene (which makes β-catenin) is almost always somatic — it arises within the tumor cells during a person’s lifetime and is not inherited. A CTNNB1 mutation does not affect family members and does not indicate FAP.

Genetic counseling and FAP screening

Because such a high proportion of CMTC cases occur in people with FAP, and because a thyroid tumor can be the first sign of this inherited syndrome, all patients diagnosed with CMTC should be referred for genetic counseling, regardless of their age or family history. If FAP is identified, colonoscopy is recommended to look for polyps in the colon, and family members will also need to be tested. Early detection and treatment of colon polyps in people with FAP greatly reduces the risk of colon cancer.

Tumor size

After the tumor is removed, it is measured in three dimensions, and the largest measurement is reported. Tumor size is important because it is used to determine the pathologic tumor stage (pT), and larger tumors are more likely to have spread to lymph nodes or beyond the thyroid.

Extrathyroidal extension

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

Microscopic extrathyroidal extension. Small amounts of tumor just beyond the thyroid, only visible under the microscope. This type does not change the tumor stage.
Gross (macroscopic) extrathyroidal extension. Tumor growth is visible during surgery or on imaging, extending into nearby structures such as the neck muscles, voice box (larynx), windpipe (trachea), or food pipe (esophagus). This type raises the tumor stage and is associated with a higher risk of recurrence.

Vascular invasion

Vascular invasion means that tumor cells have entered blood vessels in or around the tumor. Once inside a blood vessel, tumor cells can travel to distant parts of the body, such as the lungs or bones. Vascular invasion is uncommon in CMTC but, when present, is an important finding that may influence treatment and follow-up planning.

Lymphatic invasion

Lymphatic invasion means that tumor cells have entered lymphatic channels, the tiny vessels that carry a fluid called lymph toward lymph nodes. Lymphatic invasion raises the chance that nearby lymph nodes contain cancer.

Margins

A margin is the edge of the tissue removed during surgery. The pathologist examines the margins to determine whether any cancer cells extend to the cut edge.

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

Lymph nodes

Lymph nodes are small immune organs that filter lymph fluid. Cancer cells can travel from the thyroid through lymphatic channels to nearby lymph nodes. Lymph node involvement can occur in CMTC, although it is less common than in classic papillary thyroid carcinoma.

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 6. The central compartment (level 6), just around the thyroid, is the area most often sampled in thyroid cancer surgery. Lymph nodes on the same side of the neck as the tumor 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 means that cancer cells have grown beyond the outer edge (capsule) of the lymph node into the surrounding tissue.

Pathologic stage (pTNM)

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

Tumor stage (pT)

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

Nodal stage (pN)

NX: No lymph nodes were submitted for examination.
N0: No cancer was found in any of the lymph nodes examined.
N1: Cancer was found in one or more 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, and — importantly for CMTC — a genetic counselor.

Most patients are treated with surgery to remove part or all of the thyroid, often with removal of nearby lymph nodes in the central neck. The outlook for CMTC is generally excellent, and most patients are cured by surgery alone. Unlike classic papillary thyroid carcinoma, CMTC cells do not readily take up radioactive iodine, so radioactive iodine therapy is less often used. Thyroid hormone replacement is usually required after total thyroidectomy.

Because of the strong link with FAP, referral for genetic counseling is a standard part of care for all patients with CMTC. If FAP is confirmed, long-term management will include colonoscopy to screen for polyps, surveillance for other FAP-related tumors, and genetic testing for first-degree relatives. Even when FAP is not found, regular follow-up is still recommended to watch for any sign that the thyroid cancer has returned; this usually includes clinical examinations, neck ultrasound, and thyroid blood tests.

Questions to ask your doctor

Was the diagnosis of cribriform morular thyroid carcinoma confirmed by β-catenin immunohistochemistry or molecular testing?
Has an APC or CTNNB1 mutation been identified in my tumor?
Have I been referred for genetic counseling and testing for FAP?
Do I need a colonoscopy?
Should any of my family members be tested?
How large was my tumor, and did it grow beyond the thyroid?
Were any lymph nodes involved?
Were the surgical margins negative?
What is my pathologic stage (pT and pN)?
Will I need radioactive iodine therapy?
How often will I need follow-up visits, thyroid blood tests, and neck ultrasound?