Neoplasia

Types of Neoplasms

• A neoplasm is also known as a tumor, which can be benign or malignant
• Depends on the host for nutrients, blood supply, and endocrine support if hormone responsive

Benign Neoplasms

• Remain localized based on microscopic/gross characteristics
• Can be cured of disease
• Ending in "oma" (e.g., fibroma, chondroma, adenoma, papilloma)
• Determined by cell type (e.g., fibroma - tumor of fibroblasts, chondroma - derived from cartilage)

Malignant Neoplasms

• Locally aggressive and can spread to distant sites (metastasis)
• Known as cancer
• Ending in "carcinoma" or "sarcoma"
• Determined by type of tissue (e.g., carcinoma - epithelial derived, sarcoma - mesenchymal derived)

Tumor Composition

• Made of parenchyma (transformed/neoplastic cells) and stroma (connective tissue, inflammatory cells, blood vessels)
• Parenchyma determines biologic behavior, and stroma is needed for growth

Teratoma

• Type of mixed tumor containing cells from all three germ layers (ecto/meso/endoderm)
• Common in ovary and testis, can be found in oral cavity (dermoid cyst)

Pleomorphic Adenoma

• Most common salivary gland tumor (affects major and minor salivary glands)
• Exception to benign "oma" ending

Differentiation and Anaplasia

• Lack of differentiation (anaplasia) is a sign of malignancy, where cells have a backward formation
• Pleomorphism is characterized by cells and nuclei of different shapes and sizes, with prominent nucleoli
• Increased nuclear-cytoplasmic ratio, mitotic figures (may be atypical), and loss of polarity are indicative of anaplasia
• Hyperchromatism is a characteristic of anaplastic cells, where the nucleus stains dark
• Tumor giant cells are a feature of anaplasia
• Dysplasia is a disturbance of architecture and proliferative disorder that increases the risk of cancer

Benign vs Malignant Neoplasm

• Benign neoplasms will grow within and may be contained in a capsule, whereas malignant neoplasms will breakthrough the capsule and spread to other areas
• Infiltration and destruction of underlying structures are characteristic of malignant neoplasms
• Metastasis is the spread of tumor to a distant site, which can occur by blood vessels, lymphatics, or body cavities

Metastasis

• Hematogenous spread usually occurs by veins (thin-walled)
• The most frequent site of metastasis is the lungs
• Carcinomas spread by lymphatics, while sarcomas spread by hematogenous (blood) route
• Sentinel lymph node is the first node that receives lymph from the primary tumor and can be detected by injecting dye

Environmental Factors for Malignancy

• Occupational exposure, sunlight (ultraviolet light), and urban location (exposure to asbestos) are environmental factors that contribute to malignancy
• Important exposures include diet, smoking, alcohol consumption, and reproductive history
• Infectious agents, such as viral (Human papillomavirus-HPV) and bacterial (H.pylori), can contribute to malignancy

Cancer Frequency and Death Rate

• Cancer frequency increases with age
• Death rate is common between 55-75 and declines after 75
• Children are susceptible to cancer, including lymphomas, leukemias, CNS tumors, and sarcomas

Predisposing Conditions for Malignancy

• Chronic inflammatory disorders, such as inflammatory bowel disease and Barrett esophagus, can increase the risk of malignancy
• Immunodeficiency, including virus-induced malignancies, can increase the risk of malignancy
• Precursor lesions, such as squamous metaplasia/dysplasia of bronchial mucosa and endometrial hyperplasia/dysplasia, are susceptible to progressing to malignancy

Genetic Abnormalities and Cancer

• Genes affected by genetic abnormalities can contribute to malignant behavior of cancer cells
• Oncogenes promote cell growth and encode transcription factors, while tumor suppressor genes prevent uncontrolled growth
• Genes regulate apoptosis, interactions between tumor and host cells, and can be inherited or occur spontaneously
• Driver mutations can activate or inactivate protein products, leading to cancer progression

Hallmarks of Cancer

• Eight fundamental changes in cell physiology demonstrated by all cancers:
  • Self-sufficiency in growth signals
  • Insensitivity to growth-inhibitory signals
  • Altered cellular metabolism
  • Evasion of apoptosis
  • Immortality (Limitless replicative potential)
  • Sustained angiogenesis
  • Invasion & Metastasis
  • Evasion of immune surveillance

Self-Sufficiency in Growth Signals

• Oncogenes can produce own growth factors or cause stromal cells to produce growth factors
• Cell proliferation process:
  • Growth factor binds to specific receptor on membrane
  • Activation of growth receptor, activates signal-transducing proteins
  • Transmit signal across cytosol to nucleus or by cascade of signal transduction molecules
  • Activate nuclear factors that initiate & regulate DNA transcription & biosynthesis of other cellular components for cell division
  • Cell enters cell cycle for cell division
• Growth factor receptors:
  • If mutated or overexpressed, can become oncoprotein (encoded by oncogenes)
  • Examples include epidermal growth factor receptor family (EGF)-ERBB1 and ERBB2, HER2 (ERBB2) associated with breast cancers

Downstream Signal Transducing Proteins

• Cancer growth can happen with mutations to signal pathways
• Most common signal pathways involve RAS and ABL
• RAS:
  • One of the common mutated oncogenes
  • Role: stimulates proliferation regulators by altering genes that regulate growth
  • Bind GDP (guanosine diphosphate) and GTP (guanosine triphosphate)
  • RAS is inactive with GDP, becomes activated with GTP by growth factors (EGF & PDGF)
  • Becomes inactivated by losing phosphate group (reverts to GDP)
  • If stays in activated state by point mutation, will continue to send pro-growth signals
• ABL:
  • Functions as signal transducer molecule of tyrosine kinase

Nuclear Transcription Factors

• Regulate expression of growth-promoting genes
• Examples include MYC gene:
  • Activates transcription of genes including growth-promoting genes to drive cell cycle (especially cyclin-dependent kinases (CDK))
  • If altered, keep sending cells through cell cycle and enhance changes in metabolism needed for cell growth

Cell Cycle

• Four phases: Gap1-G1, Synthesis-S, Gap2-G2, and Mitosis-M
• Purpose: Cells undergo DNA replication and cell division
• Starts with G1 phase
• Enter G1 from G0 (non-active state) or after round of mitosis
• Controlled by activators and inhibitors (cyclins and cyclin-dependent kinases (CDK); checkpoints to ensure defects do not move forward (CDK inhibitors enforce checkpoints)

Checkpoints

• Checkpoint 1-G1-S: monitors health of cell and DNA integrity
• Checkpoint 2-G2-M: DNA is properly replicated before cell division takes place
• If detect irregularities, cell can repair itself, enter senescence (can’t replicate), or apoptosis
• CDK inhibitors (e.g. p16) can become defective, allow cells with damaged DNA to divide and cells at risk for malignancy

Insensitivity to Growth-Inhibitory Signals

• Tumor suppressor genes:
  • Slow down cell proliferation
  • Cause dividing cell to enter G0 phase (quiescence)
  • Can enter senescence
  • Can enter apoptosis
• Examples include:
  • RB gene
  • TP53 gene
  • Other tumor suppressors: Transforming growth factor- β (TGF-β), E-cadherin, Adenomatous polyposis coli (APC) gene

RB Gene

• Known as retinoblastoma gene, “governor” of the cell cycle
• First tumor suppressor gene to be discovered
• Regulates the G1-S checkpoint
• Inactivated for cancers to occur

TP53 Gene

• Known as “guardian of the genome”
• Most common mutated gene in cancer
• Encodes for p53 protein (transcription factor-maintains integrity of genome)
• p53:
  • Most important tumor suppressor
  • Activated when DNA damaged and promotes DNA repair (during G1 phase)
  • Role includes:
    • Place cell in quiescence
    • Induce senescence
    • Activate apoptosis
  • Mutations in DNA affect dividing cells, can lead to malignant transformation if p53 lost

Altered Cellular Metabolism

• Cancer cells utilize glycolytic pathway
• Use high levels of glucose and glutamine and increase fermentation (glucose to lactate)
• Warburg effect (aerobic glycolysis)
• Glycolytic pathway used in presence of ample oxygen
• Provides cancer cells with metabolic intermediates (rapidly dividing) for growth; mitochondrial oxidative phosphorylation does not

Autophagy

• Tumor cells can avoid process of autophagy and survive under minimum conditions

Evasion of Cell Death (Apoptosis)

• Cancer cells resistant to apoptosis by mutating genes to regulate apoptosis
• Loss of p53 and overexpression of BCL-2 family prevents apoptosis

Tumor Cell Immortality & Angiogenesis

• Can replicate endlessly (normal cells can replicate 70 times)
• Cancer cells continue with telomere maintenance
• Cells cannot enlarge beyond 1-2 mm in diameter (blood supply is needed)
• Cancer cells stimulate new blood vessel growth (neoangiogenesis)
• Provide nutrients, oxygen, endothelial cells help secrete growth factors to help stimulate growth of adjacent tumor cells

Tumor Cell Invasion

• Cancer cells invade into connective tissue by penetrating basement membrane (basal cell layer)
• Travel into connective tissue and go into vascular system by penetrating vascular basement membrane (way to metastasize to other locations)
• Circulate as single cells, can form embolus by aggregating and adhering to platelets or other blood cells
• Can be destroyed by host immune cells

Cancer Metastasis

• For metastasis to occur, need two factors:
  • Anatomic location
  • Vascular drainage of primary tumor & affinity of tumor for certain tissues
• Frequent sites of metastasis:
  • Liver
  • Lung
  • Can occur in oral cavity (soft tissue and bone)

Evasion of Immune Surveillance

• Immune surveillance-function of immune system to scan & destroy malignant cells
• Cancer antigens-expressed by cancer cells and recognized as foreign by the immune system
• Stimulate immune system and tries to prevent cancer from emerging
• Tumor cells killed by cytotoxic T cells (lymphocytes) for specific antigens
• Three broad categories of antigens:
  • Neoantigens
  • Unmutated proteins
  • Viral proteins
• Evasion of immune surveillance:
  • Tumor cells invisible to immune system
  • Tumor cells express factors that suppress or “trick” immune system
  • Tumor cells change, making it difficult for cytotoxic T cells to defend properly
  • Prevent immune checkpoints from working properly
• Immune checkpoint:
  • Main one involves PD-L1 (programmed cell death ligand 1)
  • PD-L1 expressed on surface of tumor cells
  • PD-1 receptor causes cytotoxic cells to be unresponsive and cannot kill tumor cells
  • Therapies that target these checkpoints (especially in melanoma, lung/bladder cancer)

Genomic Instability-Enabler of Malignancy

• If DNA cannot be repaired, increased risk for cancer
• Inherited disorders result of defect in DNA
• Examples include:
  • Hereditary nonpolyposis colorectal syndrome (Lynch syndrome)
  • Defect in DNA mismatch repair-cancer of cecum and proximal colon
  • Xeroderma pigmentosum
  • Autosomal recessive, defect in DNA repair (UV rays prevent normal replication)
  • Increased risk for skin cancers (squamous cell and basal cell carcinoma)
  • BRCA1 & BRCA2 genes-mutation to repair DNA by homologous recombination (develop chromosomal rearrangements and aneuploidy) susceptible to breast, ovarian, prostate cancer

Carcinogenic Agents

• Three classes of carcinogenic agents: chemicals, radiant energy (radiation), and microbes
• Chemicals: direct-acting agents (e.g. chemotherapy drugs), indirect-acting agents (e.g. polycyclic hydrocarbons, insecticides, arsenic, fungicides, nitrites)
• Radiation: ultraviolet light from sun, radiographs, radioactive elements; therapeutic radiation to head and neck can cause papillary thyroid cancer

Etiology of Cancer

• Microbes: DNA viruses (e.g. HPV, EBV, HBV), RNA viruses (e.g. HTLV-1), bacteria (e.g. H. pylori)
• Human T-cell leukemia virus type 1 (HTLV-1) causes adult T-cell leukemia/lymphoma (ATLL), targets CD4+ T cells, and has a latency period of 40-60 years
• Human Papillomavirus (HPV): low-risk types (1, 2, 4, 6, 7, 11) cause squamous papilloma and verruca vulgaris, high-risk types (16, 18, 31, 33) cause cervical, anogenital, and oropharyngeal cancer
• HPV genes E6 and E7 bind and degrade p53, stimulate expression of telomerase, and inhibit CDK inhibitor p21, leading to cell proliferation and immortality

Oropharyngeal Carcinoma

• Diagnosed with HPV-related cancer
• Vaccines can be used to prevent HPV-related cancer (e.g. Gardasil 9, Cervarix)

Effect of E6 and E7 Proteins

• Inactivate RB, p53, and p21, leading to cell proliferation and immortality

Epstein-Barr Virus

• Can cause infectious mononucleosis, oral hairy leukoplakia, Burkitt lymphoma, nasopharyngeal carcinoma, and Hodgkin lymphoma
• Virus attaches to CD21 receptor, infects B cells, and promotes B-cell proliferation through latent membrane protein 1 (LMP1)

Nasopharyngeal Carcinoma

• LMP1 expressed through NF- K B pathway
• Genetic and/or environmental factors contribute to development

Burkitt Lymphoma

• LMP1 acts as an oncogene, promoting B-cell proliferation through normal B-cell activation pathway
• Genetic and/or environmental factors contribute to development

Hepatitis B

• Causes hepatocellular carcinoma (liver cancer) through chronic inflammation, hepatocyte death, and NF- K B pathway activation

Helicobacter pylori

• Causes gastric adenocarcinoma and gastric lymphoma through chronic inflammation
• Classified as a carcinogen
• Can stimulate B-cell proliferation and promote inflammatory cytokines

Clinical Aspects of Neoplasia

• Effect on host: injury from benign/malignant tumors, damage to healthy tissues, release of hormones and procoagulants, and alteration of immune function
• Cachexia: progressive loss of body fat and lean body mass, profound weakness, anorexia, and anemia, caused by cytokines or other soluble factors produced by tumor and host

Paraneoplastic Syndrome

• Symptoms not explained by local or distant spread of tumor
• May represent earliest manifestation of occult neoplasm
• Can produce clinical illness and be lethal
• May mimic metastatic disease, commonly associated with lung, breast, and hematologic malignancies

Grading and Staging of Cancer

• Grading is based on the differentiation of tumor cells, number of mitotic figures, tumor necrosis, and presence of architectural features.
• Can be described as well, moderate, or poorly differentiated, or as low or high grade.

TNM Staging System

• T: Size of primary lesion and invasion of adjacent structures (T1-T4, T0: carcinoma in situ).
• N: Extent and spread to lymph nodes/involvement (N1-N3, N0: no nodal involvement).
• M: Presence or absence of metastasis (M0: no metastasis, M1: presence of metastasis).
• Staging has greater clinical value than grade and determines the type of treatment.

Laboratory Diagnosis

Frozen Section

• Performed during surgery, using fresh tissue.
• Evaluates margins, metastasis, and nodal involvement.
• Can be accurate but other methods are used to arrive at a final diagnosis.

Fine-needle Aspiration

• Collection of cells from a palpable tissue mass analyzed within minutes.
• Used to evaluate lymph nodes, thyroid gland, breast, and parotid.

Cytologic Smear

• Used to detect cervical cancer, fungal and viral infections (e.g., candidiasis, herpes).
• Superficial cells are collected and analyzed for abnormalities.

Excisional/Incisional Biopsy

• Used for lesions that are greater than 1 cm or suspected malignancy.
• A small piece is removed for definitive diagnosis.

Immunohistochemistry

• Used with routine H&E to accurately diagnose a specific tissue type.
• Helps with tumors that are poorly differentiated (e.g., cytokeratin markers to diagnose carcinoma).

Flow Cytometry

• Helps diagnose lymphomas and leukemias.

Tumor Markers

• Can be used as a screening tool, detect recurrence of disease, and response to therapy.
• Utilize a blood sample (e.g., prostate specific antigen (PSA) for prostate cancer).

Molecular Techniques

• Diagnose malignancy using fluorescence in situ hybridization (FISH) or PCR analysis.
• Detect minimal residual disease, help with prognosis and behavior, and determine type of therapy to use.
• Detect hereditary risk for cancer and provide genetic counseling.

Molecular Profiling

• Involves the analysis of individual genes or entire genome.
• Helps with identifying recurrent mutations in different cancers, patient care, and treatment.
• Measures all RNA expressed in cell population, proteins, and metabolites.