This article is the second of three posts that distil high‑yield ideas from the Pathology and Pharmacology chapters of First Aid for the USMLE Step 1 2026 (FA) and show how the two chapters reinforce each other at the exam level. It is meant as a roadmap and cross‑link, not a substitute for reading the full book chapters, which provide the complete tables, images, and details you’ll need for Step 1.

In this second post, we focus on neoplasia, tumor genes, cancer hallmarks, and how grade and stage help us judge tumors. 

From Dysplasia to Invasive Cancer

Dysplasia is disordered, precancerous epithelial growth, not a true adaptive response. It shows loss of uniformity in cell size and shape (pleomorphism), loss of tissue orientation, and nuclear changes such as increased nuclear‑to‑cytoplasmic ratio and clumped chromatin. Mild and moderate dysplasia do not involve the full epithelial thickness and can regress if the inciting cause is removed, whereas severe dysplasia often becomes irreversible and progresses to carcinoma in situ.

The neoplastic progression diagram (Pathology, p215) runs: normal epithelium → dysplasia → carcinoma in situ → invasive carcinoma → metastasis. Invasive carcinoma starts when cells break through the basement membrane and lose normal cell-cell adhesion, allowing tumor cells to detach and migrate.

Selected antineoplastic therapeutics in the Pharmacology chapter are linked to, for example, hematologic (hydroxyurea and methotrexate) and gastrointestinal (irinotecan) toxicities (Pharmacology, p. 246). When you review the Toxicities and Adverse Effects section tables, try to connect those toxicities back to the vulnerable normal tissues discussed here (bone marrow, GI mucosa).

Hallmarks of Cancer: What Oncogenic Mutations Achieve

Cancer is mostly caused by acquired DNA mutations affecting growth, DNA repair, and survival, but their effects can be organized into a small set of “hallmarks,” (Pathology, p217). These include growth signal self‑sufficiency, insensitivity to anti‑growth signals, evasion of apoptosis, limitless replicative potential, sustained angiogenesis, altered metabolism, immune evasion, and the ability to invade and metastasize.

Growth signal self‑sufficiency typically reflects mutations in proto‑oncogenes such as HER2, RAS, MYC, cyclins and CDKs, while anti‑growth signal insensitivity stems from mutations in tumor suppressors such as Rb and loss of E‑cadherin. Evasion of apoptosis involves genes like TP53 and BCL2, while limitless replication is supported by telomerase reactivation, which maintains telomere length and prevents senescence.

Sustained angiogenesis is driven by pro‑angiogenic factors such as VEGF, which form new, often abnormal vessels to feed the tumor. The Warburg effect describes how cancer cells favor glycolysis even with adequate oxygen, supporting biosynthesis and generating lactate, which also helps explain why cell‑cycle–active drugs preferentially injure rapidly dividing tissues like bone marrow (Pathology, p217; Pharmacology, p249). Tissue invasion and metastasis are enabled by loss of E‑cadherin, degradation of basement membrane and extracellular matrix by metalloproteinases, and altered adhesion to matrix proteins, followed by vascular dissemination and colonization of distant organs. For long‑term survival, tumor cells must escape immune attack by downregulating MHC class I, releasing immunosuppressive mediators such as TGF‑β, recruiting regulatory T cells, and hijacking immune checkpoint pathways such as PD‑1/PD‑L1 and CTLA‑4, the same pathways targeted by checkpoint-inhibitor antibodies in the Pharmacology chapter.

The hallmark of sustained angiogenesis underlies the use of anti‑VEGF and other vascular‑targeting agents, which are clinically associated with hypertension and thrombotic events (Pharmacology, p249), and impaired wound healing from vascular disruption (Pathology, p212).

Tumor Genes: Oncogenes and Tumor Suppressors

Oncogenes are mutated proto‑oncogenes that promote growth when activated, while tumor suppressor genes normally restrain proliferation or promote DNA repair and apoptosis. Exam‑relevant oncogenes include:

  • Receptor tyrosine kinases such as ALK and EGFR in lung adenocarcinoma and HER2/ERBB2 in breast and gastric cancers.
  • Non‑receptor kinases such as BCR‑ABL in CML and some ALL, JAK2 in myeloproliferative neoplasms, and BRAF (serine/threonine kinase) in melanoma, colorectal carcinoma, papillary thyroid carcinoma, and hairy cell leukemia.
  • Transcription factors like MYC family members in Burkitt lymphoma and neuroblastoma.
  • Cytokine receptor mutations such as c-KIT (CD117) in GI stromal tumors and mastocytosis.
  • RAS GTPases such as KRAS in pancreatic, colorectal, lung, and endometrial cancers.
  • Anti‑apoptotic proteins such as BCL‑2 in follicular and diffuse large B‑cell lymphomas.

Key tumor suppressors include APC (WNT/β‑catenin pathway) in familial and sporadic colorectal cancer; BRCA1/2 (DNA repair) in breast, ovarian, prostate, and pancreatic cancers; CDKN2A encoding p16, which blocks G1→S phase; NF1, NF2, and PTEN in various nervous system and endocrine tumors; RB1, which inhibits E2F and controls the G1→S phase; TP53, which activates p21 and halts the cell cycle after DNA damage; TSC1/2, VHL, and WT1, each associated with specific inherited cancer syndromes.

Together, these gene tables show how gain‑of‑function changes in growth drivers and loss‑of‑function changes in brakes cooperate to generate the hallmarks described above (Pharmacology, p220). You will meet kinase inhibitors (often ending in -tinib or -rafenib) in the Pharmacology chapter, where their toxicities are detailed (Pharmacology, p254).

How we “Judge” Tumors: Grade and Stage

Once a tumor is identified, Pathology distinguishes grade from stage. Grade describes the degree of differentiation and mitotic activity, ranging from low‑grade (well‑differentiated) to high‑grade (poorly differentiated or anaplastic). Higher grade usually correlates with more aggressive behavior.

Stage describes how far the tumor has spread. It reflects depth of local invasion and the presence of nodal or distant metastases, usually summarized by the TNM staging system: T for primary tumor size/invasion, N for nodal involvement, and M for distant metastasis. The key message is that stage generally carries more prognostic weight than grade.

TNM stage determines prognosis and helps guide how aggressive cancer therapy needs to be (Pathology, p216). Later Pharmacology sections build on this by showing how TNM stage shapes treatment intensity.

Aging: Normal Change Versus Disease

The chapter also asks you to recognize normal aging as a time‑dependent progressive decline in organ function, driven by factors such as telomere shortening, DNA methylation changes, and mitochondrial dysfunction. Typical findings include increased cardiovascular arterial stiffness and valve calcification, sarcopenia and osteopenia, skin atrophy with wrinkles and senile purpura, reduced brain volume with mild cognitive decline, impaired accommodation and hearing, and reduced renal mass, GFR, and hormonal function. Lipofuscin, the yellow‑brown “wear and tear” pigment seen in multiple organs, is another classic marker of normal aging.

These changes are not diseases in themselves, but they increase vulnerability to pathology and alter drug distribution, metabolism, and excretion, so standard doses can produce higher plasma drug concentrations and older patients often need lower maintenance doses. Regimens are, therefore, individualized based on renal, hepatic, and overall functional status, particularly in older adults, when you review antineoplastic and immunomodulatory drugs and their toxicities in the Toxicities and Adverse Effects tables (Pharmacology, p229, p246).

Next up is Blog 3 where we focus on how the Pharmacology chapter’s drug mechanisms and toxicity content build on these cancer themes.

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