STEPTRACKERGENERAL PRINCIPLES | PATHOLOGY | HIGH-YIELD REVIEW

Benign vs Malignant & Nomenclature

Neoplasia is monoclonal, unregulated growth. The name tells you the tissue of origin and how it behaves.

FOCUS ON
Metastasis is the one feature that proves malignancy. Carcinoma means epithelium, sarcoma means mesenchyme. Watch the "-oma" names that are malignant. A neoplasm is monoclonal and hyperplasia is polyclonal — and exams test this with G6PD isoforms and κ:λ ratios.
TISSUE OF ORIGIN
BENIGN
MALIGNANT
NOTE
Epithelium
surface, glands
Adenoma (glandular), papilloma (finger-like)
Carcinoma: adenocarcinoma, squamous cell carcinoma, urothelial carcinoma
Carcinomas usually spread by lymphatics first
Fat
Lipoma
Liposarcoma
Sarcomas usually spread through blood
Smooth muscle
Leiomyoma
Leiomyosarcoma
Fibroid uterus is the most common benign tumor in women
Skeletal muscle
Rhabdomyoma (cardiac, with tuberous sclerosis)
Rhabdomyosarcoma
Rhabdomyosarcoma: most common soft-tissue sarcoma in children
Bone & cartilage
Osteoma, chondroma
Osteosarcoma, chondrosarcoma
Detail on pages 17.04–17.05
Blood vessels
Hemangioma
Angiosarcoma
Hemangioma: common in infants, often regresses
Blood & lymphoid cells
— (no benign counterpart)
Leukemia, lymphoma, myeloma
"Lymphoma" is always malignant
Melanocytes
Nevus (mole)
Melanoma
"Melanoma" is always malignant
Germ cells
Mature cystic teratoma (ovary)
Immature teratoma, seminoma/dysgerminoma, yolk sac tumor, choriocarcinoma
Seminoma is malignant despite the name
Mesothelium
—
Mesothelioma
Asbestos exposure
Look-alikes
not true neoplasms
Hamartoma: disorganized normal tissue in its usual site (lung "coin lesion")
Choristoma: normal tissue in the wrong site (pancreatic rest in stomach)
Neither invades or metastasizes

Mechanism — from mutation to metastasis

DNA damageOncogene ↑ · suppressor ↓
→
Clonal expansionMonoclonal
→
Dysplasia→ carcinoma in situ
→
InvasionBasement membrane crossed
→
MetastasisDefines malignancy
Hallmarks of cancer
Own growth signals · ignore stop signals · evade apoptosis · limitless replication (telomerase) · angiogenesis (VEGF)
… and more
Invasion and metastasis · immune evasion (PD-L1) · aerobic glycolysis (Warburg effect) · genomic instability

Benign vs malignant features

FEATURE
BENIGN
MALIGNANT
Growth
Slow, expansile, often encapsulated
Rapid, infiltrative
Differentiation
Well — resembles parent tissue
Variable → anaplasia
Nuclei
Uniform, low N:C ratio
Pleomorphic, hyperchromatic, high N:C, big nucleoli
Mitoses
Few, normal
Many, atypical
Invasion
None
Through basement membrane
Metastasis
Never
Possible — the hallmark

How it's tested

COMMON CONFUSIONLymphoma, melanoma, mesothelioma and seminoma end in "-oma" but are all malignant. A hamartoma is not a true neoplasm.
THE TRAPA lymph node whose B cells all express κ light chain is monoclonal, which means lymphoma. A uterine mass expressing a single G6PD isoform is a leiomyoma, not hyperplasia.
YOUR APPROACHName = tissue of origin + behavior. To decide behavior, look for invasion and metastasis. To decide neoplasm vs hyperplasia, look at clonality.

If you see… think…

One feature that proves malignancy → metastasis
Lymph node with κ-only (light-chain restricted) B cells → monoclonal → lymphoma
Single G6PD isoform in a uterine mass → monoclonal leiomyoma
Lung coin lesion with "popcorn" calcification, cartilage + epithelium → hamartoma
Pancreatic tissue in the gastric wall → choristoma (ectopic rest)
Smooth-muscle tumor with necrosis and many mitoses → leiomyosarcoma
Carcinomas that spread through blood → RCC, HCC, follicular thyroid, choriocarcinoma
Cystic ovarian mass with hair and teeth in a young woman → mature teratoma (benign)
Loss of polarity, high N:C, atypical mitoses → anaplasia