Thyroid Carcinomas

Slide 1 · THYROID CARCINOMAS

A clinicopathologic framework

Cell of origin · molecular drivers · morphology · clinical behavior

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning outcomes: Recognize and distinguish thyroid cancers

Classify major carcinomas by cell of origin and differentiation.

Connect MAPK, PI3K/AKT, and RET alterations with tumor phenotype.

Recognize the decisive morphologic findings in papillary, follicular, and medullary carcinoma.

Explain why invasion, dissemination route, and molecular progression matter.

Slide 3 · Cell of origin defines two fundamentally different groups

Follicular epithelium gives rise to most thyroid carcinomas.

Papillary, follicular/oncocytic, and aggressive high-grade carcinomas belong to this lineage.

Parafollicular C cells give rise to medullary thyroid carcinoma.

Thyroid follicular cell

Parafollicular C cell

Papillary carcinoma

Follicular / oncocytic

High-grade / anaplastic

Medullary carcinoma

Slide 4 · Increasing detection does not imply parallel lethality

Small, localized carcinomas are frequently detected incidentally by palpation or ultrasonography.

The textbook documents substantial historical increases in diagnosis after ultrasound screening programs.

Overall mortality remained low because many detected tumors, especially papillary carcinomas, have excellent outcomes.

Slide 5 · Relative frequency is strongly dominated by papillary carcinoma

Subtype

Approximate share in textbook

Interpretation

Papillary

~85%

Commonly differentiated; often incidental

Follicular / oncocytic

~5–15%

Follicular lineage; invasion-based diagnosis

High-grade differentiated / PDTC

~5%

Less frequent; clinically aggressive

Anaplastic

~1%

Uncommon; disproportionately lethal

Medullary

~5%

Distinct C-cell lineage

Slide 6 · Well-differentiated and aggressive carcinomas behave differently

Most follicular-derived cancers are well differentiated.

Poorly differentiated or anaplastic tumors may acquire additional molecular alterations during progression.

Aggressive follicular-derived and medullary carcinomas account for a substantial share of thyroid cancer mortality.

Differentiated carcinoma

Generally favorable

High-grade differentiated / PDTC

More aggressive

Anaplastic carcinoma

Very poor prognosis

Slide 7 · MAP-kinase signaling is a central oncogenic axis

RTK activity engages downstream RAS and BRAF signaling.

MEK and ERK transmit growth-factor signals to the nucleus.

Mutations or fusion kinases can drive constitutive signaling without normal upstream control.

RTK / fusion kinase

RAS–GTP

BRAF

MEK

ERK

Proliferation / differentiation

Slide 8 · The PI3K/AKT axis provides a second growth program

PI3K/AKT pathway alterations occur in a subset of follicular carcinomas.

PTEN normally restrains PI3K pathway signaling.

Activating PIK3CA or inactivating PTEN lesions release growth/survival signaling.

RTK / RAS

PI3K

PDK1 / AKT

Growth / survival

PTEN inhibits PI3K signaling

Slide 9 · Driver patterns differ across major thyroid tumor classes

Tumor context

Characteristic molecular alterations

Conceptual consequence

Conventional PTC

BRAF V600E; RET, NTRK, BRAF fusions

MAPK-pathway activation

Follicular-pattern neoplasms

RAS mutations; PAX8::PPARG fusion

Follicular/RAS-like phenotype

Progressed high-grade tumors

Additional TP53; TERT promoter lesions

Dedifferentiation / aggressiveness

Medullary carcinoma

RET activating point mutations

C-cell oncogenesis

Slide 10 · BRAF V600E promotes constitutive MAPK activation

BRAF encodes a serine/threonine kinase downstream of RAS.

V600E substitutes glutamate for valine at codon 600 and produces gain of function.

The textbook associates this alteration with reduced expression of thyroid differentiation markers and possibly higher recurrence risk.

RTK / fusion kinase

RAS–GTP

BRAF

MEK

ERK

Proliferation / differentiation

Slide 11 · RET and NTRK fusions activate receptor kinases in PTC

Chromosomal rearrangement

Constitutively active fusion kinase

MAPK signal activation

Papillary tumor growth

Schematic mechanism; Arrows indicate conceptual sequence

Slide 12 · Radiation-associated PTC often has gene fusions

Ionizing radiation is a major thyroid-cancer risk factor, especially during childhood or adolescence.

Radiation can induce DNA double-strand breaks and structural rearrangements.

Fusion kinases are particularly relevant in radiation-associated and some childhood papillary carcinomas.

Slide 13 · RAS alterations characterize many follicular neoplasms

RAS mutations occur across follicular adenoma, carcinoma, and NIFTP-related lesions.

RAS-like tumors often preserve expression of follicular differentiation markers.

A follicular architectural phenotype does not establish benignity or malignancy.

Colloid-containing follicles (schematic)

Slide 14 · PAX8::PPARG rearrangement characterizes a follicular subset

T(2;3) rearrangement

PAX8::PPARG fusion gene

Altered follicular-cell transcriptional program

Subset of follicular neoplasms

Schematic mechanism; Arrows indicate conceptual sequence

Slide 15 · PIK3CA activation or PTEN loss occurs in follicular carcinoma

PIK3CA encodes a catalytic component of PI3K.

PTEN is a tumor suppressor antagonizing the PI3K signaling pathway.

Alterations in a subset of follicular carcinomas, not in every case.

RTK / RAS

PI3K

PDK1 / AKT

Growth / survival

PTEN inhibits PI3K signaling

Slide 16 · High-grade evolution involves acquisition of additional hits

High-grade, poorly differentiated, and anaplastic cancers often share earlier drivers with well-differentiated cancers.

Additional TP53 and TERT promoter mutations are enriched in aggressive lesions.

Progression is possible, not inevitable, for a differentiated carcinoma.

Differentiated PTC / FTC

Additional alterations: TP53, TERT promoter

High-grade / poorly differentiated / anaplastic

Slide 17 · RET alterations have lineage-specific mechanisms

RET fusions in papillary carcinoma differ from RET activating point mutations in medullary carcinoma.

Familial medullary carcinoma is associated with germline activating RET mutations.

Somatic RET mutations are found in many sporadic medullary carcinomas.

RET activation

PTC: RET fusions

MTC: RET point mutation

Distinct mechanisms in distinct lineages

Slide 18 · Environmental risk factors have subtype associations

Ionizing radiation

Dietary iodine deficiency

Exposure during the first two decades is particularly important.

Papillary carcinomas predominate after such exposure.

Fusion-generating chromosomal breaks are implicated.

Associated with greater frequency of follicular neoplasms.

Follicular carcinomas comprise a larger relative share in deficient regions.

Association does not identify the histologic diagnosis.

Slide 19 · NIFTP is deliberately not classified as invasive cancer

NIFTP was formerly termed noninvasive encapsulated follicular variant of PTC.

It has a follicular pattern and PTC-like nuclear features but lacks invasion under strict diagnostic criteria.

Histologic assessment after surgery is required to make the definitive designation.

Intact capsule

Invasive growth

NIFTP (requires strict criteria)

Invasive EFV-PTC

Slide 20 · Most thyroid carcinomas first present as nodules

An asymptomatic thyroid mass is a common initial presentation.

A cervical lymph node can be the first manifestation of papillary carcinoma.

Clinical palpation alone usually cannot reliably separate benign from malignant nodules.

Slide 21 · Voice and airway symptoms signal possible advanced disease

Hoarseness raises concern for local invasion or involvement of structures controlling vocal-fold motion.

Dysphagia, cough, or dyspnea can reflect compressive or infiltrative growth.

Rapid enlargement with obstructive symptoms is especially concerning for anaplastic carcinoma.

Slide 22 · Nodule evaluation combines clinical, biochemical, and cytologic data

TSH is relevant to the decision to use radionuclide scintigraphy.

Ultrasonography helps characterize nodules and guides sampling when indicated.

Fine-needle aspiration cytology is important, with molecular tests useful for indeterminate results.

Thyroid nodule

Clinical context + TSH

Ultrasonography / FNA when appropriate

Cytology ± molecular assessment

Slide 23 · A “hot” nodule is usually not malignant

Papillary carcinomas as usually scintigraphically “cold.”

Hyperfunctioning “hot” nodules are almost never malignant.

Scintigraphy is generally reserved for a low TSH rather than ordered for every thyroid nodule.

Slide 24 · Fine-needle aspiration cannot prove follicular invasion

Follicular adenoma and minimally invasive follicular carcinoma are cytologically indistinguishable.

The malignant criterion is capsular and/or vascular invasion in histologic sections.

Surgical tissue and extensive capsule sampling are therefore essential for classification.

Tumor follicles

Focal capsular transgression

Schematic

Slide 25 · Dissemination patterns provide a mechanistic diagnostic clue

Conventional papillary carcinomas frequently invade lymphatics and spread to cervical lymph nodes.

Follicular carcinomas prefer hematogenous dissemination to distant organs.

The pattern reflects differences in invasive behavior, not an absolute rule.

Papillary carcinoma

Follicular carcinoma

Lymphatic spread

Vascular spread

Cervical nodes

Bone / lung / other

Slide 26 · Papillary carcinoma dominates the clinical workload

Papillary thyroid carcinoma is the most common primary thyroid malignancy.

Presentation most often between ages 25 and 50.

Prior ionizing radiation exposure is a particularly relevant association.

Slide 27 · Papillary carcinoma may be solitary or multifocal

Grossly, some lesions are well circumscribed; Others infiltrate surrounding parenchyma.

Fibrosis, calcification, cystic change, and papillary cut-surface foci may occur.

Gross appearance alone does not replace microscopic nuclear evaluation.

Slide 28 · True papillae have fibrovascular cores

Branching papillae contain a vascular connective-tissue stalk.

Cuboidal neoplastic epithelium covers the cores in one or more layers.

Architecture is useful, but papillary-type nuclear morphology remains essential.

Epithelial lining

Fibrovascular core

Schematic branching papilla

Slide 29 · Papillary carcinoma nuclei display chromatin clearing

Finely dispersed chromatin produces a pale or optically empty nuclear appearance.

The classic descriptor is “Orphan Annie eye” nucleus.

A constellation of nuclear findings is more reliable than one isolated feature.

Cleared chromatin

Nuclear groove

Pseudoinclusion

Schematic nuclear appearances; Not a histologic specimen

Slide 30 · Nuclear grooves and pseudoinclusions are diagnostic clues

Nuclear membrane irregularities may produce grooves or wrinkling.

Intranuclear cytoplasmic pseudoinclusions represent invagination of cytoplasm.

These are cytomorphologic findings—not evidence of a separate viral inclusion process.

Cleared chromatin

Nuclear groove

Pseudoinclusion

Schematic nuclear appearances; Not a histologic specimen

Slide 31 · Psammoma bodies are lamellated calcifications

Concentric calcified bodies may occur in papillary cores or adjacent stroma.

Psammoma bodies strongly suggest papillary thyroid carcinoma when found in FNA material.

They are uncommon in typical follicular and medullary carcinomas.

Concentric lamellated calcification

Schematic; Not an H&E image

Slide 32 · Papillary carcinoma favors lymphatic dissemination

Lymphatic tumor invasion is often present microscopically.

Regional cervical lymph node metastases are relatively common.

Lymph node involvement must be interpreted in the context of overall stage and recurrence risk.

Papillary carcinoma

Follicular carcinoma

Lymphatic spread

Vascular spread

Cervical nodes

Bone / lung / other

Slide 33 · PTC clinical course often remains favorable

Many tumors present as asymptomatic nodules or incidentally detected small masses.

A 10-year survival exceeding 95% in PTC.

Long-term surveillance remains relevant because recurrence may occur despite favorable mortality.

Slide 34 · Papillary carcinoma prognosis depends on extent and host factors

Older age is associated with less favorable prognosis in the source.

Extrathyroidal extension indicates invasion beyond the thyroid.

Distant metastasis is an important determinant of stage and outcome.

Slide 35 · Treatment intensity follows recurrence-risk profile

Selected lower-risk disease

Higher recurrence-risk disease

Lobectomy alone may provide excellent outcomes in appropriate patients.

Preservation of endocrine function can be advantageous.

Avoiding unnecessary surgical morbidity matters.

May require total thyroidectomy.

Radioactive iodine is used in appropriately selected patients.

Risk stratification precedes treatment choice.

Slide 36 · Thyroid surgery involves functional trade-offs

Lobectomy preserves contralateral thyroid tissue.

More extensive thyroid surgery may increase risks such as vocal cord palsy from recurrent laryngeal nerve injury.

Pathology and recurrence risk help determine the appropriate extent of surgery.

Slide 37 · Follicular carcinoma is defined by invasion

Cells may form well-differentiated follicles resembling normal thyroid.

Capsular penetration and/or vascular invasion differentiates carcinoma from adenoma.

Bland nuclei and follicle formation do not guarantee benign behavior.

Tumor follicles

Focal capsular transgression

Schematic

Slide 38 · Follicular carcinoma often forms a solitary mass

Nodules may be sharply circumscribed or widely infiltrative.

Cut surfaces range from gray/tan to pink and may be colloid-rich.

Large cancers can penetrate the capsule and invade the surrounding neck.

Slide 39 · Follicular carcinoma may resemble ordinary thyroid tissue

Uniform follicular cells often surround lumina containing colloid.

Typical PTC nuclear features are absent in conventional follicular carcinoma.

Psammoma bodies are not expected.

Colloid-containing follicles (schematic)

Slide 40 · Capsular invasion requires careful histologic scrutiny

The critical observation is complete transgression of the tumor capsule by neoplastic tissue.

Sampling must distinguish true invasion from an irregular but intact capsule.

Adequate capsule examination is necessary to avoid underdiagnosis.

Tumor follicles

Focal capsular transgression

Schematic

Slide 41 · Vascular invasion establishes follicular malignancy

Tumor infiltration into venous channels within or immediately beyond the capsule is significant.

Its identification cannot be made with aspirated free cells alone.

Vascular access explains the preference for hematogenous metastasis.

Tumor cells within capsular vessel

Schematic; Histologic confirmation required

Slide 42 · Minimal versus extensive invasion changes prognosis

Minimally invasive carcinoma

Widely invasive carcinoma

May have low recurrence risk.

10-year survival exceeding 90%.

Extent of invasion and stage require histologic assessment.

Frequently demonstrates extension into thyroid or beyond.

May present with distant metastatic disease.

Associated with substantially worse long-term outcome.

Slide 43 · Follicular carcinoma spreads predominantly through blood

Regional lymphatic nodal involvement is typically less conspicuous than in PTC.

Distant sites include bone, lung, liver, brain, and others.

Clinical staging must consider remote organs, not just cervical nodes.

Papillary carcinoma

Follicular carcinoma

Lymphatic spread

Vascular spread

Cervical nodes

Bone / lung / other

Slide 44 · Iodine handling and thyroglobulin inform follow-up

Differentiated follicular-derived tumor deposits may take up radioactive iodine.

TSH suppression with thyroid hormone is described to limit trophic stimulation of residual tumor.

After total thyroidectomy, circulating thyroglobulin can help monitor persistent or recurrent differentiated disease.

Slide 45 · Oncocytic carcinoma is a follicular-lineage variant

Oncocytic tumor cells have abundant granular eosinophilic cytoplasm.

Oncocytic cytology alone does not establish malignant behavior.

The distinction between oncocytic adenoma and carcinoma still depends on invasive features.

Slide 46 · NIFTP arose from outcome-driven reclassification

Historically, encapsulated noninvasive follicular-variant tumors were labeled carcinomas.

With strict absence of invasion, their risk of recurrence or metastasis is extremely low.

The NIFTP label avoids treating all such lesions as biologically equivalent to invasive carcinoma.

Slide 47 · NIFTP retains a follicular pattern with PTC-like nuclei

Follicles form the dominant architecture rather than conventional branching papillae.

Nuclei show enlargement, clearing, and membrane abnormalities reminiscent of PTC.

The decisive distinction is strict absence of invasion after tissue sampling.

Intact capsule

Invasive growth

NIFTP (requires strict criteria)

Invasive EFV-PTC

Slide 48 · Invasive encapsulated follicular variant PTC is malignant

Invasive EFV-PTC shares some nuclear and molecular similarities with NIFTP.

Capsular, vascular, or intrathyroidal invasion invalidates a NIFTP diagnosis.

Vascular invasion explains potential hematogenous dissemination.

Intact capsule

Invasive growth

NIFTP (requires strict criteria)

Invasive EFV-PTC

Slide 49 · Follicular-pattern lesions require a structured differential

Entity

Nuclear phenotype

Invasion

Follicular adenoma

No characteristic PTC-type nuclear features

Absent

Follicular carcinoma

Usually lacks PTC-type nuclear features

Capsular / vascular

NIFTP

PTC-like nuclear features

Absent under strict criteria

Invasive EFV-PTC

PTC-like nuclear features

Present

Slide 50 · The capsule is both an anatomic and diagnostic boundary

An intact capsule around a follicular neoplasm does not prove carcinoma.

Transcapsular or vascular invasion provides decisive malignant evidence.

The distinction influences terminology, prognosis, and treatment intensity.

Tumor follicles

Focal capsular transgression

Schematic

Slide 51 · Some thyroid tumors lose follicular differentiation

High-grade differentiated and poorly differentiated carcinomas show aggressive histologic features.

Anaplastic carcinoma largely loses recognizable thyroid follicular morphology.

The source associates progressive aggressiveness with acquired molecular alterations.

Differentiated carcinoma

Generally favorable

High-grade differentiated / PDTC

More aggressive

Anaplastic carcinoma

Very poor prognosis

Slide 52 · High-grade thyroid tumors may show necrosis and mitoses

Tumor necrosis and increased mitotic activity are high-grade features.

Poorly differentiated carcinomas may grow as solid, insular, or trabecular nests.

These appearances warrant careful distinction from ordinary well-differentiated carcinoma.

Slide 53 · Poorly differentiated carcinoma has insular growth

Solid, insular (nested), and trabecular arrangements replace many familiar follicles.

A patient may present like a lower-grade thyroid cancer until histology reveals aggressive features.

The extent of necrosis or mitotic activity informs pathologic interpretation.

Slide 54 · Anaplastic carcinoma has marked morphologic heterogeneity

Cells can appear epithelioid, spindle-shaped, markedly pleomorphic, or giant-cell rich.

Some tumors mimic squamous carcinoma or a mesenchymal malignancy.

Foci of differentiated thyroid carcinoma may coexist and support progression.

Slide 55 · Anaplastic tumors often lose follicular lineage markers

Dedifferentiation may remove expression of follicular thyroid differentiation proteins.

Earlier oncogenic driver mutations can remain detectable despite loss of phenotype.

Molecular ancestry and current histology are different lines of evidence.

Differentiated PTC / FTC

Additional alterations: TP53, TERT promoter

High-grade / poorly differentiated / anaplastic

Slide 56 · Anaplastic carcinoma often produces an airway emergency

The presentation is frequently a rapidly enlarging bulky cervical mass.

Local invasion produces dyspnea, dysphagia, cough, or hoarseness.

Many patients have extension beyond the thyroid or lung metastases at diagnosis.

Slide 57 · Aggressive tumors dominate thyroid-cancer mortality

Anaplastic thyroid carcinoma has an exceptionally poor prognosis.

High-grade differentiated and poorly differentiated carcinomas fare better than anaplastic lesions, but worse than typical PTC.

Biologic grade and invasion pattern are essential alongside anatomic stage.

Differentiated carcinoma

Generally favorable

High-grade differentiated / PDTC

More aggressive

Anaplastic carcinoma

Very poor prognosis

Slide 58 · Medullary carcinoma originates from parafollicular C cells

C cells are calcitonin-producing neuroendocrine cells distinct from thyrocytes.

Medullary carcinoma may show nests, trabeculae, or occasionally follicle-like arrangements.

Its biomarkers and inherited predisposition differ from follicular-derived cancer.

Thyroid follicular cell

Parafollicular C cell

Papillary carcinoma

Follicular / oncocytic

High-grade / anaplastic

Medullary carcinoma

Slide 59 · Medullary carcinoma may be sporadic or MEN2-associated

Sporadic disease

Inherited MEN2 disease

Most medullary carcinomas arise sporadically in adulthood.

Somatic activating RET mutations occur in many cases.

A solitary tumor is the common presentation.

Germline activating RET mutations underlie predisposition.

Bilateral or multicentric tumors are common.

C-cell hyperplasia may be evident nearby.

Slide 60 · RET point mutations drive medullary thyroid tumorigenesis

Constitutively active RET receptor signaling promotes C-cell neoplasia.

Germline activation predisposes to inherited medullary carcinoma.

RET fusion oncogenes typical of some PTCs are not the medullary mechanism.

RET activation

PTC: RET fusions

MTC: RET point mutation

Distinct mechanisms in distinct lineages

Slide 61 · Medullary carcinoma is often infiltrative and nonencapsulated

Gross tumors are often firm and pale gray-tan.

Sporadic lesions are commonly solitary, whereas syndromic cases may be bilateral and multicentric.

Larger masses may show hemorrhage, necrosis, and extrathyroidal extension.

Slide 62 · Amyloid in medullary carcinoma derives from calcitonin

Neoplastic cells may be polygonal or spindle-shaped and arranged in nests or trabeculae.

Intercellular stromal amyloid deposits derive from calcitonin-related polypeptides.

This is a biologically meaningful secretory product rather than follicular colloid.

Neuroendocrine tumor nests

Stromal amyloid

Simplified schematic

Slide 63 · Calcitonin and CEA support medullary monitoring

Calcitonin is produced by tumor cells and is valuable diagnostically and postoperatively.

Carcinoembryonic antigen (CEA) is an additional useful tumor marker.

Marked calcitonin elevation does not usually cause prominent hypocalcemia.

Slide 64 · C-cell hyperplasia is an inherited-predisposition clue

Multiple C-cell clusters in thyroid tissue may precede medullary carcinoma in MEN2.

The contralateral lobe may show hyperplasia even when the dominant cancer is unilateral.

This finding should raise suspicion for inherited disease, including when family history is absent.

Neuroendocrine tumor nests

Stromal amyloid

Simplified schematic

Slide 65 · Medullary tumors may secrete multiple peptide hormones

Some lesions elaborate vasoactive intestinal peptide and cause diarrhea.

Ectopic corticotropin secretion may cause a Cushing syndrome.

Secretory symptoms can occasionally precede recognition of the thyroid mass.

Slide 66 · A hereditary RET mutation changes family management

MEN2-associated medullary carcinoma may develop at very young ages.

Identification of a germline RET mutation informs familial risk assessment.

The source describes prophylactic thyroidectomy in asymptomatic carriers, with timing influenced by the RET variant.

Slide 67 · Biomarkers answer different pathologic questions

Marker / alteration

Tumor context

Main interpretive role

BRAF V600E

Conventional PTC

Molecular driver; tumor characterization

RAS / PAX8::PPARG

Follicular-pattern tumors

Molecular phenotype; not proof of invasion

TP53 / TERT promoter

Aggressive follicular-derived tumors

Progression-associated changes

Thyroglobulin

Differentiated follicular-derived tumors

Selected postoperative surveillance

Calcitonin / CEA

Medullary carcinoma

Tumor identification / monitoring

Slide 68 · The subtype comparison has three decisive axes

Subtype

Defining pathology

Common spread / clinical clue

Papillary

Nuclear clearing; grooves; papillae; psammoma

Lymphatic → cervical nodes

Follicular

Capsular and/or vascular invasion

Hematogenous → distant organs

Anaplastic

Highly pleomorphic and undifferentiated

Rapid infiltrative neck mass

Medullary

C-cell neuroendocrine tumor; amyloid

Calcitonin / CEA; MEN2 association

Slide 69 · Histology and genotype must be interpreted together

Cell lineage

Architecture + nuclear features

Invasion and grade

Risk and molecular context

Schematic mechanism; Arrows indicate conceptual sequence

Slide 70 · Case: Cervical node with papillary-type nuclei

Teaching vignette (fictional): A patient presents with a cervical node and a small thyroid nodule.

Cytology demonstrates optically clear nuclei, grooves, and psammoma bodies.

Question: Which carcinoma and likely route of spread best explain the findings?

Discuss the explanation before advancing

Slide 71 · Case resolution: Nuclear phenotype outweighs size

Papillary-type nuclear features and psammoma bodies favor papillary carcinoma.

Regional nodal presentation is consistent with lymphatic dissemination.

Even small primary tumors can present with a cervical nodal metastasis.

Slide 72 · Case: Follicular tumor with bland aspirate

Teaching vignette (fictional): FNA shows a cellular follicular neoplasm without convincing PTC-type nuclei.

A resection specimen demonstrates tumor penetration through its capsule.

Question: Why did FNA not determine whether this was carcinoma?

Discuss the explanation before advancing

Slide 73 · Case resolution: The invasive front carries the diagnosis

Follicular carcinoma may closely resemble adenoma cytologically.

Histologic documentation of capsular and/or vascular invasion establishes malignancy.

Complete or extensive capsule sampling is therefore diagnostically necessary.

Tumor follicles

Focal capsular transgression

Schematic

Slide 74 · Case: Bilateral tumors with stromal amyloid

Teaching vignette (fictional): Multifocal thyroid masses contain nested tumor cells and eosinophilic stromal amyloid.

A relative has a history of an endocrine tumor.

Question: Which tumor lineage and hereditary mechanism should be considered?

Discuss the explanation before advancing

Slide 75 · Case resolution: Consider MEN2 beyond the thyroid

Amyloid with a neuroendocrine thyroid neoplasm supports medullary carcinoma.

Multifocal/bilateral disease and C-cell hyperplasia suggest an inherited predisposition.

Germline RET status has implications for relatives and preventive care.

Slide 76 · Five discriminators anchor thyroid carcinoma diagnosis

Diagnostic discriminator

Inference supported

Papillary-type nuclear findings ± psammoma bodies

Papillary carcinoma is favored

Capsular / venous invasion in follicular tumor

Follicular carcinoma rather than adenoma

Follicular growth + PTC-like nuclei; no invasion

NIFTP when strict criteria are satisfied

Necrosis / mitoses / undifferentiated morphology

Consider high-grade or anaplastic disease

C-cell neuroendocrine tumor + amyloid

Medullary carcinoma is favored

Slide 77 · Final synthesis: Morphology explains clinical behavior

Cell of origin separates medullary carcinoma from follicular-derived malignancies.

The decisive morphologic discriminator is often nuclear phenotype, invasion, or dedifferentiation.

Molecular alterations explain biologic lineage, signaling, and sometimes progression—but do not replace histology.

Thyroid follicular cell

Parafollicular C cell

Papillary carcinoma

Follicular / oncocytic

High-grade / anaplastic

Medullary carcinoma

Slide 78 · Primary reference and verification limits

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th edition (2026). Chapter 24: The Endocrine System, pp. 988–993.

Working source: project-supplied chapter text and adjacent thyroid carcinoma subsection excerpts.

The corresponding original chapter PDF and its diagnostic photomicrographs were not provided; all drawings here are editable conceptual schematics, not specimens.