Malignant Tumors

Characteristics

Malignant tumors, A.K.A cancers have specific characteristics not found in benign tumors.

• Form Metastasis (this is the most telling feature of a malignant tumor)
• Invasive growth, no capsule
• Undifferentiated, may barely resemble the tissue or organ if at all
• Atypical cellular features
• Abnormally fast growth
• Frequent Necrosis (not enough blood supply)

Atypical Cellular Features Explained

• Anaplasia: poorly differentiated
• Pleomorphism: wide variation in shape or appearance of tumor cells
• Hyperchromatic: Nucleus: the nucleus stains darker than normal
• High Nucleus to Cytoplasm Ratio
• Prominent nucleoli

What’s in a Name

Cancers are named according to their origin. Some cancers have specific names, like Burkitt’s lymphoma, Hodkin’s disease, and Wilm’s tumor

Carcinoma

Carcinoma: a malignant tumor of epithelial cell origin

Types of Carcinomas

Squamous cell carcinoma: occurs in the skin, mouth, and or esophagus

Adenocarcinoma: from glandular tissue (GI mucosa, endometrium)

Transitional cell carcinoma: Transitional epithelium (urinary tract)

Sarcoma

Sarcoma: cancer of the muscle, bone, connective tissue, or fat

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Types of Sarcomas

Leiomyosarcoma: cancer of the smooth muscle (uterus)

Rhabdomyosarcoma: cancer of the skeletal muscle

Osteosarcoma: cancer of the bone

Chondrosarcoma: cancer of the cartilage

Liposarcoma: cancer of fatty tissue

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Teratomas

Teratoma: germ cell (ovary/testis) layer-derived tumor can have bone, and teeth, and rarely form outside the ovary/testis but can happen if it develops from stem cells. Often benign or not.

• Immature teratoma: malignant usually in the male’s testis
• Mature teratoma: benign, usually females

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Biological Behavior of Cancers

Invasion

Benign lesions have a capsule and grow by pushing other tissues around them aside. Malignant tumors don’t care about borders and grow right into other tissues.

Metastasis

Metastasis is the most important sign of malignancy.

Tumors grow and become vascularized. Tumors can grow into vessels. Tumor cells become loose and are swept with the blood or lymphatic stream into other tissues where they get stuck or may form islands of new tumor growth. Tumors frequently have particular (favorite) routes of metastasis. Carcinomas frequently travel through the lymphatics. Sarcomas like to travel through the blood. Metastasis frequently targets the liver, lungs, brain, lymph nodes, and bone marrow.

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Clinical Manifestations

Symptoms

Symptoms of cancer due to the location include painless swelling, “tumors”, obstructions, easy bleeding, change in color or consistency, edema, and change in body function.

Symptoms of cancer due to features of the tumor include wasting, anemia, infection, and hormonal changes (hormone abnormalities (gigantism)).

• Wasting: AKA Cachexia is the cancer typical weight-loss, weakness, and loss of appetite (anorexia)

Paraneoplastic Syndromes

• Hypercalcemia: cancer makes a parathyroid hormone (PTH) like protein.
• Hormone-like effects: hypoglycemia (insulin-like), Cushing-Syndrome (ACTH-like substance secreted lung cancer).
• Neurologic Abnormalities: antibodies associated with lung cancer
• Skin Changes: acanthosis nigricans (hyperpigmentation of the skin in the groin, neck, and axilla (armpit)).

Why do people die from cancer?

Cancer may interfere with the body's function (obstruction, destruction of vital tissue, space-occupying lesions). It may lead to bleeding. It may produce substances (ie hormones) that alter the function of tissues.

Cancer-Induced Cachexia and Anorexia

Cancer-Induced cachexia and anorexia are seen in 50% of patients

Cachexia results in the loss of muscles and adipose tissue ONLY. It is not known why this occurs but prognostically very important.

Death is imminent with 30-35% weight loss.

Highest levels in gastric and pancreatic cancer.

Lowest levels in lymphomas, sarcomas, breast cancer

Cancer cells can affect lipid and protein metabolism. Cancer can produce substances such as lipolysis and proteolysis-inducing factors and cytokines (TNF and IL-6) (cellular communication signals) that can affect lipid and protein metabolism.

The loss of muscle mass results in respiratory failure of patients (hypostatic pneumonia due to immobility)

Cancer patients eat less (anorexia = loss of appetite)

Increased nutrition cannot overcome cancer-induced cachexia

Diagnosis

Clinical signs of diagnosis: visible tumor, bleeding, unexplained weight loss, etc.

Abnormal Diagnostic tests such as x-ray, CT, MRI, biopsy

Lab test: abnormal CBC, PSA, CEA

Diagnosis and identification can be difficult because it may resemble other conditions (infections, benign conditions, etc)

Monoclonality

Monoclonality: cancer cells are clones of a singular cancer cell

“Tumor stem cells” - in some cancers, there are so-called “tumor-inducing” cells that basically are cancer stem cells. The cells renew themselves and may be more easily transformed into cancer.

If a neoplasm is monoclonal there is a higher likelihood of cancer

if a neoplasm is polyclonal there is a lower likelihood of cancer

Example: Lymphoma

-B Cell Lymphomas express only 1 kappa or lambda light chain so benign accumulations of B cells will have both present.

-T Cell Leukemias are monoclonal (all the T-cells have the same T-cell receptor (this can be checked using PCR)), if an accumulation is polyclonal it is most likely not cancer but an infection, inflammation, or other causes.

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