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A 55-year-old man presents with increasing fatigue, 15-pound weight loss, and a microcytic anemia. Colonoscopy identifies a mass in the ascending colon, and biopsy specimens reveal well-differentiated colorectal cancer (CRC). He undergoes surgical resection and is found to have high-risk stage III CRC with five positive lymph nodes. After surgery, he feels entirely well with no symptoms. Of note, he has no other illnesses. What is this patient’s overall prognosis? Based on his prognosis, what are the possible benefits of adjuvant chemotherapy? How long should he receive adjuvant chemotherapy? The patient receives a combination of 5-fluorouracil (5-FU), leucovorin, and oxaliplatin (FOLFOX) as adjuvant therapy. One week after receiving the first cycle of therapy, he experiences significant toxicity in the form of myelosuppression, diarrhea, and altered mental status. What is the most likely explanation for this increased toxicity? Is there any role for genetic testing to determine the etiology of the increased toxicity?

In 2020, approximately 1.8 million new cancer cases will be diagnosed in the USA, and nearly 606,000 individuals are expected to die from this disease. Cancer is the second most common cause of death in the United States, accounting for 1 in 4 deaths. It is a disease characterized by a defect in the normal control mechanisms that govern cell survival, proliferation, and differentiation. Cells that have undergone neoplastic transformation usually express cell surface antigens that may be of normal fetal type, and they may display other signs of apparent immaturity. They may exhibit qualitative or quantitative chromosomal abnormalities, including various translocations, fusions, and the appearance of amplified gene sequences. It is now well established that a small subpopulation of cells, referred to as tumor stem cells, reside within a tumor mass. They retain the ability to undergo repeated cycles of proliferation as well as to migrate to distant sites in the body to colonize various organs in the process called metastasis. Such tumor stem cells have clonogenic (colony-forming) capability, and they are characterized by chromosome abnormalities reflecting their genetic instability, which leads to progressive selection of subclones that can survive more readily in the multicellular environment of the host. This genetic instability provides cancer cells with the ability to become resistant to radiotherapy and to systemic therapies, including cytotoxic chemotherapy, targeted therapy, and immunotherapy. The invasive and metastatic processes as well as a series of metabolic abnormalities associated with the cancer result in tumor-related symptoms and eventual death of the patient unless the neoplasm can be eradicated with treatment.


The incidence, geographic distribution, and behavior of specific types of cancer are related to multiple factors, including sex, age, race, genetic predisposition, and exposure to environmental carcinogens. Of these factors, environmental exposure is probably most important. Exposure to ionizing radiation has been shown to be a significant risk factor for several cancers, including acute leukemias, thyroid cancer, breast cancer, lung ...

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