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PDQ: Acronym for Physicians Data Query database of clinical trials past and present for all types of cancer maintained by the National Cancer Institute.
Palliative Care: Treatment aimed at relieving symptoms and pain rather than effecting a cure.
Pancytopenia: A decrease below normal in the concentration of the three major blood cell types: red cells, white cells and platelets.
Paroxysmal Nocturnal Hemoglobinuria (PNH): An uncommon disorder characterized by an increased rate of break-down of red blood cells and decreased production of white blood cells and platelets. This leads to excretion of the red blood pigment, hemoglobin, in the urine, particularly at night. The increased sensitivity of red cells to damage is frequently accompanied by a failure of blood cell production, called aplastic anemia. The disease is a clonal disorder and is related to other clonal diseases of the marrow. There may be an increase in the propensity to evolve into acute myelogenous leukemia.
Performance Status: The performance status semi-quantifies the ability of a patient to perform daily activities. This semi-quantification is very helpful in clinical trials in assessing the state of health of patients under treatment. If one group has a significant difference in their performance status, the interpretation of treatment results will be influenced. The performance status also plays a role in determining whether a patient can tolerate intensive therapy. The following short version of the definition of activities level describes the performance status in terms of a scale decreasing from normal activities and capabilities. Other versions use percent of normal as an indicator.
0 Normal Activity
1 Symptoms but ambulatory
2 In bed < 50 percent of time
3 In bed greater than >50 percent of time
4 100 percent bedridden
Petechiae: Pin-head-sized sites of bleeding in the skin. This type of bleeding results from a very low platelet count. The small punctate hemorrhages are frequently seen on the legs, feet, trunk and arms. They evolve from red to brown and are eventually disappear. They stop developing when the platelet count increases.
Phagocytes: Cells that readily eat (ingest) microorganisms like bacteria or fungi and can kill them as a means of protecting the body against infection. The two principal phagocytes are neutrophils and monocytes. They emigrate out of the blood and into tissues in which an infection has developed. A severe decrease in the blood level of these cells is the principal cause of susceptibility to infection in patients treated with intensive radiotherapy and/or chemotherapy. The latter treatments suppress blood cell production in the marrow resulting in deficiencies of these phagocytic cells.
Philadelphia or Ph Chromosome: The name applied to the abnormality of the chromosome number 22 in the marrow and blood cells of patients with chronic myelogenous leukemia. The abnormality reflects a shortened long arm of chromosome number 22. The observation was reported first by physicians at the University of Pennsylvania and named the Philadelphia chromosome. Since its discovery, the piece of chromosome lost has been shown to stick (translocate) to chromosome 9 in most cases. Indeed, some of chromosome 9 sticks (translocates) to chromosome 22. This is referred to as a balanced translocation, because virtually equal lengths of partial chromosome arms exchange position. Because chromosome 22 is a very short chromosome and chromosome 9 is a very long chromosome, the addition to chromosome 9 was less apparent than the shortening of 22 until more sensitive techniques became available. The abnormality of chromosome 22 is now usually abbreviated to the Ph chromosome.
Plasma Cell: A cell that is derived from the antigen-induced activation and maturation of B-lymphocytes. It is the principal antibody producing form of B-cells. In myeloma, the tumor cell has the appearance of plasma cells, that is, they are malignant plasma cells, sometimes referred to as myeloma
Plasma Cell Leukemia: The presence of frequent plasma cells in the blood in a patient with myeloma.
Plasmacytoma: A localized tumor of malignant plasma cells, either in a bone or in the other tissues of the body. If there is only one such area of bone involved it is called solitary plasmacytoma. An area outside of bone may be referred to as extramedullary plasmacytoma.
Platelet Transfusion: The transfusion of donor platelets may be required to treat or prevent bleeding in patients treated with high-dose chemotherapy or radiotherapy who develop severe platelet deficiency. The platelets can be pooled from several unrelated donors and given as “pooled random-donor platelets.” It requires the platelets from at least six one-unit blood donors to significantly raise the platelet count in a recipient. Sufficient platelets can be obtained from one donor by hemapheresis. The latter technique skims off the platelets of large volumes of blood passing through the hemapheresis machine. The red cells and plasma are returned to the donor. The advantage of single donor platelets is that the patient is not exposed to the antigens on platelets from many different people and is less likely to develop antibodies against donor platelets. HLA-matched platelet transfusion can be given from a related donor with an identical or very similar HLA tissue type. The platelets are collected by hemapheresis.
Platelets: Small blood cells (about one-tenth the volume of red cells) that stick to the site of blood vessel injury, aggregate with each other and seal off the injured blood vessel to stop bleeding. Thrombocyte is a synonym for platelet and is often used as the prefix in terms describing disorders of platelets, such as thrombocytopenia or thrombocythemia.
Polycythemia Vera: A clonal disease characterized by the over-production of blood cells by a mutant multipotential hematopoietic stem cell in the marrow. The hallmark of the disease is an increased number of red cells. The number of white blood cells and platelets are also usually increased. The accumulation of red cells is progressive and usually requires treatment at the time of diagnosis. The increase in white cells is usually slight but the increase in platelets may become troublesome and require treatment as well.
Polymerase Chain Reaction (PCR): A technique to expand trace amounts of DNA or RNA so that the specific type of the DNA or RNA can be studied or determined. This technique has become useful in detecting a very low concentration of residual leukemia or lymphoma cells, too few to be seen using a microscope. The technique can detect the presence of one leukemic cell among five hundred thousand to one million non-leukemic cells. PCR requires a specific DNA (or RNA) abnormality or marker, like an oncogene, in the leukemic or lymphomatous cells for its use to identify residual abnormal cells.
Portacath: A form of central venous line in which the whole of the line is surgically implanted within the body. A membrane just below the skin gives access by a simple skin puncture to a line running straight into one of the main blood vessels. This simplifies the administration of chemotherapy.
Precursor Cell: A series of developing marrow cells in each blood cell lineage that terminates development in a mature blood cell. Erythroblasts are precursors of the red cell. Myelocytes are precursors of the neutrophil, and megakaryocytes are precursors of the platelet. The precursor cells can be distinguished by inspection of stained marrow films with the light microscope.
Prevalence: Represents new and pre-existing cases of a disease alive on a given date. Prevalence is a function of both the incidence of the disease and survival with the disease. Thus, the annual incidence of a disease in the United States may be 30,000/ total population per year (new cases that year) but the prevalence of that disease may be 200,000/total population per year (new cases plus preexisting cases from prior years).
Progenitor Cell: An immature cell in the marrow that can be isolated by growing suspensions of marrow cells in culture dishes with added growth factors. Depending on the factors added, one can identify progenitors of each blood cell lime age by the appearance of the colonies of cells that proliferate from a single progenitor cell. Progenitor cells are referred to as colony-forming units or cells, CFU or CFC. The specific lineage is indicated by a suffix, such as CFU-E(erythrocytic), CFU-eo (eosinophilic), CFU-meg (megakaryocytic), etc. The progenitors mature into precursors that mature into blood cells.
Prolymphocytic Leukemia: A type of Chronic Lymphocytic Leukemia in which the malignant T-cells have a more immature appearance. The disease is usually more rapidly progressive than classical Chronic Lymphocytic Leukemia.
Protocol: A schedule of treatment developed for a clinical trial. The drugs, dose of drugs, frequency of administration and route of administration are specified.
Pruritis: Itching, which may be a significant problem in polycythemia, Hodgkin lymphoma, and less often other lymphomas.
Purging: The process by which tumor cells are removed from the marrow or blood stem cell suspension that are to be used for an autologous transplant. The stem cells used in an autologous transplant are obtained from a patient with leukemia, lymphoma, or myeloma. The patient is usually treated to induce a remission before the stem cells are harvested but some inapparent tumor cells are probably always present. Purging is used to try to minimize the chance of returning tumor cells to the patient with the stem cells infusion after intensive and hopefully curative cytotoxic treatment is given.
Purpura: The presence of skin bleeding. This may be in the form of black and blue patches of varying sizes (ecchymoses) or pin-head-sized spots called petechiae or both.