1. Benign vs Malignant Tumors

Key distinguishing features – DLM

• D – Differentiation & anaplasia

(How similar/abnormal the cells look + behave)

• L – Local invasion

(Benign = no invasion; Malignant = infiltrates neighbours)

• M – Metastasis

(Only malignant tumors spread to distant sites)

Growth rate

• Rapid growth not always malignancy
• Some cancers grow slowly → growth rate unreliable alone

Clinical importance

• Benign diagnosis reassures patients
• Helps counsel anxiety + guide treatment urgency

Clinical classification

• Usually accurate based on appearance + behaviour
• Some tumors remain difficult to categorize

Definitions

• Differentiation: resemblance to normal cells (structure + function)
• Anaplasia: lack of differentiation

Microscopy differences

• Benign
• Well-differentiated
• Rare, normal mitoses
• Examples: lipoma, chondroma
• Malignant
• May be poorly differentiated
• NOTE: some cancers well differentiated but malignant due invasion/metastasis
• Example: well-differentiated thyroid adenocarcinoma

Tumor stroma (not diagnostic)

• Supplies blood
• Stroma amount influences hardness

Desmoplasia

• Dense fibrous stroma induced by cancers
• Tumors with desmoplasia = scirrhous (“stony hard”)

2. Anaplasia

Meaning

• "Backward formation" → loss of differentiation
• May originate from:
• Stem cells failing to differentiate
• Dedifferentiation of mature cells

Key fact

• Anaplasia = reliable indicator of malignancy
• Undifferentiated tumors are always malignant

Morphologic features — PLANT-G

• Pleomorphism(variation in size and shape of cells and nuclei within the same tumor.)
• Loss of polarity- loss of the normal orderly arrangement of cells relative to the basement membrane.
• Atypical mitoses (tripolar/quadripolar spindles)
• Nuclear abnormalities (hyperchromasia, ↑ N:C ratio)
• Tumor giant cells
• Giant nucleoli

Nucleus:cytoplasm ratio

• Normal = 1:4 to 1:6
• Anaplastic = close to 1:1

Tumor giant cells

• Very large, with huge or multiple nuclei

Loss of polarity

• Disordered architecture
• Glands/layers disappear

3. Tumor Function & Differentiation

Functional behaviour

• Well-differentiated tumors:
• Retain specialized functions
• Anaplastic tumors:
• Lose specialized functions

Retained function examples — HEK

• Hepatocellular carcinoma → bile
• Endocrine tumors → hormones
• Keratin production in squamous carcinoma

Unexpected tumor functions

• Tumors may express:
• Fetal proteins
• Ectopic hormones

Ectopic hormones = hormones produced by non-endocrine tumors

Examples in lung carcinoma:

• ACTH
• PTH-like peptide
• Insulin
• Glucagon

4. Dysplasia & Carcinoma in Situ

Dysplasia definition

• Disordered epithelial proliferation
• Loss of uniformity + orientation

Microscopic features

• Pleomorphism
• Hyperchromatic nuclei
• Abnormal mitoses
• Loss of architectural maturation

Mitoses location

• Normal squamous epithelium:
• confined to basal layer
• Dysplasia:
• mitoses throughout epithelium

Architectural disruption

• Normal sequence (basal → squamous maturation) lost

Carcinoma in situ

• Full-thickness dysplasia
• No basement membrane invasion
• Pre-invasive cancer

Clinical significance

• Dysplasia ≠ cancer
• Dysplasia, especially mild/moderate, may regress
• Often seen adjacent to cancers → marker of increased cancer risk

Mnemonic Recap

• DLM – Differentiation, Local invasion, Metastasis
• PLANT-G – Anaplasia features
• HEK – functional retained tumors

Key conceptual summary for revision

• Benign tumors stay local & resemble normal tissue.
• Malignant tumors invade, metastasize, and show anaplasia.
• The poorer the differentiation → the worse the behaviour.
• Dysplasia is a warning sign; carcinoma in situ = cancer “in place.”
• Invasion marks transition to true malignancy.