7.2 about 26 minDeep Learning viewL7 p.3–4, 14, 22

Benign or malignant: differentiation, dysplasia and invasion

Malignancy is decided by behavior: invasion and metastasis. Differentiation, growth rate and the basement membrane tell you how close a tumor is to that line, and a handful of acquired capabilities explain how it crosses it.

Four features that separate benign from malignant

L7 p.3–4, 22

The lecture compares benign and malignant tumors on differentiation, rate of growth, local invasion and metastasis. The first three are tendencies; metastasis is the one feature that defines malignancy without exception, because benign tumors never metastasize.

Benign versus malignantL7 p.3–4, 22

  • Differentiation

    Benign
    Well differentiated; looks like the tissue of origin; nuclei of normal size and shape
    Malignant
    Ranges from well differentiated to anaplastic; pleomorphic, hyperchromatic nuclei

  • Rate of growth

    Benign
    Usually slow, expansile
    Malignant
    Usually fast; varies with differentiation

  • Local invasion

    Benign
    Pushes; often a fibrous capsule (uterine leiomyoma is circumscribed without one)
    Malignant
    Infiltrates; no capsule; ragged borders; often necrosis

  • Metastasis

    Benign
    Never
    Malignant
    Frequent; the decisive criterion

  • Clinical feel

    Benign
    Well circumscribed, mobile
    Malignant
    Poorly circumscribed, fixed to surrounding structures

Growth rate needs perspective. A tumor must go through about 30 population doublings to reach 1 g (about 10⁹ cells), the smallest mass that is usually detectable clinically; ten more doublings make 1 kg. By the time a cancer is found, most of its life history, and many of its mutations, lie behind it. Some tissues resist invasion well (mature cartilage, the elastic tissue of arteries), so the route a tumor takes is not random.

Worked calculation · How many doublings make a detectable tumor?

Starting point
1 transformed cell
Cells in 1 g of tumor
≈ 10⁹
Cells in 1 kg of tumor
≈ 10¹²

Formula

cells after n doublings = 2ⁿ

L7 p.4

Differentiation and anaplasia

L7 p.3, 22

Differentiation is how closely tumor cells resemble the normal cells they came from, in shape and in function. Anaplasia is the lack of differentiation, and it is a hallmark of malignancy. A well-differentiated squamous carcinoma still makes keratin pearls; an anaplastic one is a sheet of bizarre cells that no longer reveals its origin.

Teaching schematic

  1. 1. Well differentiated

    Uniform cells and nuclei, low N:C ratio, orderly, few mitoses: resembles the tissue of origin.

  2. 2. Moderately differentiated

    Nuclei larger and darker, some variation, more mitoses, order partly lost.

  3. 3. Poorly differentiated (anaplastic)

    Pleomorphism, hyperchromasia, N:C ratio up to 1:1, atypical mitoses, loss of polarity and necrosis (pale patch).

From well differentiated to anaplastic. As differentiation is lost, nuclei enlarge and darken, vary in size and shape, crowd the cytoplasm and divide abnormally, and the cells lose their orderly arrangement.L7 p.3, 22

What anaplasia looks like, and whyL7 p.4, 22

  • Pleomorphism

    What you see
    Cells and nuclei vary in size and shape, giant cells
    What it reflects
    Unstable genome; no single program of maturation

  • Hyperchromasia

    What you see
    Dark, coarsely clumped chromatin
    What it reflects
    Extra DNA (aneuploidy) and active transcription

  • High N:C ratio

    What you see
    Nucleus nearly as large as the cell (up to 1:1)
    What it reflects
    Growth outpaces maturation

  • Atypical mitoses

    What you see
    Many mitoses, some tripolar or bizarre
    What it reflects
    Uncontrolled proliferation; defective checkpoints

  • Loss of polarity

    What you see
    Disorderly sheets instead of orderly layers
    What it reflects
    Cells no longer respond to positional cues

  • Necrosis

    What you see
    Pink, nuclear-debris-filled zones, often in the center of large nodules
    What it reflects
    Growth outruns the new, leaky blood supply

The lecture also describes the poorly differentiated cell from the inside: fewer mitochondria, less prominent rough ER, and loss of cadherins, the adhesion molecules that hold epithelial cells together. Losing cadherins lets cells slip away into the surrounding tissue, the first step of invasion (7.3).

Dysplasia → carcinoma in situ → invasion

L7 p.8, 22L1 p.28

In epithelium, malignancy usually announces itself before it invades. Dysplasia is disordered growth: the cells show atypia (enlarged, hyperchromatic nuclei, a high N:C ratio), lose their orderly maturation and divide above the basal layer. When these changes involve the full thickness of the epithelium, the lesion is carcinoma in situ (CIS): it has the cytology of cancer, but the basement membrane is intact, so it has not invaded and cannot yet metastasize.

Teaching schematic

  1. basement membrane (intact)

    1. Dysplasia

    Atypia in the lower layers; maturation still visible at the surface. Basement membrane intact.

  2. basement membrane (intact)

    2. Carcinoma in situ

    Atypia through the full thickness, no maturation. Basement membrane still intact: cannot metastasize.

  3. basement membrane (breached)

    3. Invasive carcinoma

    Cells cross the basement membrane into stroma, where lymphatics and veins are.

The same epithelium at three moments. Low-grade dysplasia: atypia in the lower layers, maturation preserved at the surface. Carcinoma in situ: atypia through the full thickness, no maturation, basement membrane intact. Invasive carcinoma: tumor cells cross the basement membrane into the stroma, where lymphatics and veins are waiting.L7 p.8L1 p.28

The basement membrane is the line that matters because the epithelium has no lymphatics or blood vessels of its own. Above it, a clone can only grow; below it, it meets the vessels that carry it away. That is why carcinoma in situ, even when its cells look fully malignant, is cured by complete local excision, and why the first stromal invasion changes the prognosis.

Case image

Skin biopsy: atypical keratinocytes with enlarged nuclei through the full thickness of the epidermis, a few round pink apoptotic cells (arrows), and an intact lower border.
Skin, squamous cell carcinoma in situ (from the midterm simulation, Q5): atypical keratinocytes with large nuclei fill the full thickness of the epidermis, with no maturation toward the surface, yet the lower border is smooth and unbroken. The arrows mark apoptotic tumor cells; even cancers keep some apoptosis, through the intrinsic pathway.Midterm sim. p.2

Morphology comparison · Layers

Where are the cells?

Three schematics of the same squamous epithelium at one scale: epithelium above, stroma with a lymphatic and a vein below. Switch the overlays on and off, then decide which specimen is invasive and what the evidence is.
  1. Specimen A: squamous epithelium over stroma (teaching schematic)

    Specimen A

  2. Specimen B: squamous epithelium over stroma (teaching schematic)

    Specimen B

  3. Specimen C: squamous epithelium over stroma (teaching schematic)

    Specimen C

Teaching schematics, not micrographs. Orange outline: lymphatic. Red outline: small vein.

1 of 3

Which specimen shows invasion?

2 of 3 · answer the previous question first

Specimen A has severe atypia through its full thickness. Why is it not invasive?

3 of 3 · answer the previous question first

In specimen C, which finding establishes invasion?

0 of 3 answered correctly. Source: Lesson 7 Neoplasia, pp. 8 and 22; the same distinction is tested in Ch. VII Q2 and Midterm sim. Q5–Q6.

Core activity · Almost Twins

Almost Twins

Two look-alikes side by side. Decide what they share, then pick the clue that separates them and say why it works.

Look-alike A

Dysplasia (low grade)

basement membrane (intact)
Cervical epithelium, HPV positive (schematic).
  • Atypical nuclei: enlarged, hyperchromatic, high N:C ratio
  • Atypia confined to the lower layers; cells still mature toward the surface
  • Basement membrane intact
  • Often regresses, especially after HPV clearance

Step 1 · What they share

What do these two epithelia share?

Select every feature that both show.

Tumor Pathology Case Lab

Ch. VII cases p.3, 5, 6L7 p.8, 22–25

Four specimens from the lecture and the Chapter VII cases, worked the way a pathologist works them: look at the slide before you read anything, decide whether the basement membrane has been crossed, choose the stain that answers the open question, sort the report into grade and stage, then take one more clue and say what it changes.

Centerpiece · Tumor Pathology Case Lab

Tumor Pathology Case Lab

Four specimens, each worked the way a pathologist works: look first, decide whether the basement membrane has been crossed, choose the stain that answers the question, sort the findings into grade and stage, then take one more clue and say what it changes.
Bronchial biopsy: irregular nests of atypical squamous cells in stroma; one nest surrounds a bright pink, concentric whorl of keratin.
Bronchial biopsy, H&ECh. VII cases p.5

Clinical history

A 60-year-old man has 4 months of weight loss, wheezing and breathlessness. He has smoked two packs a day for 40 years. A chest radiograph shows a 10-cm mass in the left lung, and bronchoscopy shows the left main bronchus obstructed. A biopsy is taken.

Before you answer, look for

  • Are the cells arranged in nests, glands or sheets?
  • Is anything being made by the cells: keratin, mucin, matrix?
  • Are the nests confined to an epithelial layer, or sitting in stroma?
  1. 1. Look first
  2. 2. Has it invaded?
  3. 3. Choose a stain
  4. 4. Grade or stage
  5. 5. One more clue

Step 1 · Look first

What do you call this, and what is the lineage clue?

Decide benign or malignant first, then name what the cells are making.

Cervical dysplasia: the model sequence

L7 p.14Midterm sim. p.2Ch. VII cases p.3

The cervix shows the whole sequence in one organ. High-risk human papillomavirus (HPV 16 and 18) infects the immature metaplastic cells of the transformation zone. Its first visible sign is koilocytic atypia: squamous cells with a clear perinuclear halo and a wrinkled, dark nucleus, the cytopathic effect of the virus. When viral oncoproteins disable the cell's brakes (section 7.5), the epithelium becomes dysplastic, graded as CIN 1 (lower third), CIN 2 (up to two thirds) and CIN 3 (full thickness, the same as carcinoma in situ). Invasion through the basement membrane makes invasive squamous cell carcinoma.

Case image

Cervical biopsy: squamous epithelium crowded with dark, elongated nuclei through most of its thickness, little maturation toward the surface, and a smooth, unbroken lower border with the stroma.
Cervical biopsy (midterm simulation, Q6): crowded cells with dark, elongated nuclei occupy most of the epithelial thickness, polarity is lost and the cells barely mature toward the surface. The lower border with the stroma is smooth: dysplasia, not invasion.Midterm sim. p.2

Lecture image

Pap smear: large flat squamous cells with small nuclei, neutrophils, and one cell (arrow) with a large, dark, irregular nucleus filling much of the cell.
A Pap smear: mature superficial and intermediate cells have small nuclei and abundant cytoplasm; the dysplastic cell (arrow) has a large, dark, irregular nucleus that fills much of the cell, a high N:C ratio. Screening finds cells like this years before invasion.L7 p.14

Worked case · One specimen, two answers

A 25-year-old woman's Pap smear shows koilocytes; biopsy shows invasive squamous cell carcinoma, HPV positive. In the hysterectomy specimen, beside the invasive focus, dysplastic cells occupy the entire thickness of the epithelium with no maturation, and the basement membrane there is intact.

What is the lesion in the areas with an intact basement membrane, and why does the distinction matter in the same uterus?

Ch. VII cases p.3

The hallmarks: what a clone must acquire

L7 p.3–4, 15, 19

Every malignant tumor has acquired a small set of capabilities, each from a different kind of mutation or adaptation. The lecture names several of them; the others come from the gene classes in 7.4. Think of the list as the answer to 'what must change before a clone can invade and spread?'

Teaching schematic

  • Growth without a signal

    Oncogenes: RAS, ERBB2

  • Ignoring the brakes

    RB and p53 lost

  • Not dying

    BCL2 overexpressed

  • Dividing forever

    Telomerase reactivated

  • Building a blood supply

    Hypoxia → HIF-1α → VEGF

  • Rewired metabolism

    Aerobic glycolysis (Warburg) → FDG-PET

  • Hiding from the immune system

    MHC I ↓, PD-L1, CTLA-4, DAF

  • Invading and spreading

    E-cadherin ↓, MMPs (7.3)

  • Accumulating mutations faster

    DNA repair genes lost

Hallmarks of cancer, each paired with its mechanism and the lecture's example.L7 p.3–4, 15, 19

Limitless replication (telomerase). Every division shortens telomeres, and normal somatic cells eventually stop dividing (senescence) when telomeres get too short. Germ cells and stem cells express telomerase, which rebuilds telomeres. Most cancers reactivate it, so the clone can divide indefinitely. The lecture links telomerase to avoiding apoptosis; more precisely, it prevents the senescence and chromosomal crisis that short telomeres would cause.

Angiogenesis (VEGF). Oxygen diffuses only about 1–2 mm from a capillary, so a tumor cannot grow beyond that size without new vessels. Hypoxia in the tumor stabilizes HIF-1α, which switches on vascular endothelial growth factor (VEGF); tumor cells also release proteases that break down the vessel basement membrane so endothelial cells can migrate. The new vessels are leaky and disorganized, which is why large tumors still have areas of necrosis.

Altered metabolism (the Warburg effect). Cancer cells take up large amounts of glucose and run glycolysis even when oxygen is plentiful (aerobic glycolysis). Glycolysis yields little ATP, but its intermediates are the carbon skeletons for new lipids, nucleotides and amino acids, which a dividing cell needs. Clinically this is what PET sees: the radiolabeled glucose analogue FDG is taken up and trapped in the tumor, which is why PET is used for diagnosis, staging and monitoring.

Immune evasion. Cytotoxic T cells recognize tumor antigens on MHC class I, so tumors that downregulate MHC I escape them (natural killer cells, which kill cells lacking MHC I, are the backup). Many tumors also express PD-L1, which binds PD-1 on T cells and switches them off, and they exploit CTLA-4, a T-cell receptor that blocks costimulation. Antibodies that block PD-1, PD-L1 or CTLA-4 ('checkpoint inhibitors') release this brake. The lecture adds decay-accelerating factor (DAF): tumor cells limit C3 and C5 convertases, so complement cannot assemble the membrane attack complex on them.

Knowledge check · 7.2

Answer, read why, and try again whenever you like. Answers are kept in both study modes.

0 of 6 correct
  1. Q1Carcinoma in situCh. VII cases p.3L7 p.22

    A 25-year-old woman's Pap smear shows koilocytic atypia. Biopsy shows invasive squamous cell carcinoma, HPV positive, and she undergoes hysterectomy. Besides the invasive focus, the pathologist finds dysplastic squamous cells occupying the entire thickness of the cervical epithelium with no maturation; the basement membrane in these areas is intact.

    Which term best describes these areas?

  2. Q2Telomerase in cancerCh. VII cases p.2L7 p.4

    A 25-year-old man has a painless, enlarged left testis that does not transilluminate. Serum AFP and hCG are normal. Orchiectomy shows embryonal carcinoma.

    Compared with normal adult somatic cells, this germ-cell tumor is most likely to express high levels of which protein?

  3. Q3Cervical dysplasiaMidterm sim. p.2L1 p.28

    A 33-year-old woman has an abnormal Pap smear. On cervical biopsy the epithelium lacks normal polarity; individual cells have hyperchromatic nuclei and a high nucleus-to-cytoplasm ratio, and the tissue is disorderly. The lower border of the epithelium is smooth.

    Cervical biopsy: squamous epithelium crowded with dark, elongated nuclei through most of its thickness, little maturation toward the surface, and a smooth, unbroken lower border with the stroma.

    Which term best describes these changes?

  4. Q4Warburg effect and PETL7 p.3

    A 61-year-old man with a lung mass has an FDG-PET scan. The mass and two mediastinal nodes take up the tracer intensely.

    Why do the tumor cells accumulate FDG?

  5. Q5Immune evasion: PD-1/PD-L1L7 p.4Ref. · Robbins: immune evasion

    A patient with metastatic melanoma responds dramatically to an antibody against PD-1. Biopsies before treatment showed tumor cells with strong PD-L1 expression surrounded by inactive T cells.

    What did the antibody do?

  6. Q6AngiogenesisL7 p.4

    A carcinoma nodule grows to about 1–2 mm and then stops enlarging for months. Which change most likely allows it to grow again?

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