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Paraneoplastic syndromes (PNSs) are neoplasm-associated alterations in bodily structure or function or both that occur distant to the tumor. They are an extremely diverse group of clinical aberrations that are associated with the noninvasive actions of the tumor. In many situations, the PNS parallels the underlying malignancy, and therefore, successful treatment of the tumor leads to disappearance of the PNS. Alternatively, recurrence of the PNS after successful treatment signals recurrence of the tumor, and the return of the PNS often significantly precedes the detectable recurrence of the tumor. This is often the case with paraneoplastic hypercalcemia, often referred to as hypercalcemia of malignancy (HM). The most common cause of hypercalcemia in dogs is cancer. Neoplasia is diagnosed in approximately two-thirds of dogs with hypercalcemia vs. approximately one-third in cats. A variety of tumors have been associated with HM. Lymphoma is the most common cause of HM, and the most common anatomical site for dogs with lymphoma-associated HM is the cranial mediastinum. Other tumors associated with HM in dogs and cats include anal sac apocrine gland adenocarcinoma, thyroid carcinoma, multiple myeloma, bone tumors, thymoma, squamous cell carcinoma, mammary gland carcinoma/adenocarcinoma, melanoma, primary lung tumors, chronic lymphocytic leukemia, renal angiomyxoma, and parathyroid gland tumors. As HM is a potential medical emergency, the primary goal in cases of HM is the elucidation of the underlying cause and thereby instituting the appropriate specific therapy., (Copyright © 2012 Elsevier Inc. All rights reserved.)

The immune system is generally divided into 2 primary components: the innate immune response, and the highly specific but more slowly developing adaptive or acquired immune response. Immune responses can be further separated by whether they are induced by exposure to a foreign antigen (an "active" response) or whether they are transferred through serum or lymphocytes from an immunized individual (a "passive" response). The ideal cancer immunotherapy agent should be able to discriminate between cancer and normal cells (ie, specificity), be potent enough to kill small or large numbers of tumor cells (ie, sensitivity), and lastly be able to prevent recurrence of the tumor (ie, durability). Tumor immunology and immunotherapy is one of the most exciting and rapidly expanding fields at present.

P-glycoprotein (p-gp) is a transmembrane protein functioning as a drug-efflux pump in the intestinal epithelium. Human patients with inflammatory bowel disease (IBD) who fail to respond to treatment with steroids express high levels of p-gp in lamina propria lymphocytes. The purpose of this study was to investigate p-gp expression in duodenal biopsy samples of dogs with chronic enteropathies and to evaluate the expression of p-gp after treatment with a known inducer of p-gp (prednisolone). Duodenal biopsy samples from 48 dogs were evaluated immunohistochemically with the mouse monoclonal antibody C219 for expression of p-gp in lamina propria lymphocytes. Biopsy samples were available from 15 dogs after treatment with prednisolone and 16 dogs after dietary therapy alone ("elimination diet"). Treatment with prednisolone resulted in an increase in p-gp expression (P=0.005). In contrast, dietary treatment alone produced no significant change in p-gp expression (P=0.59). A low p-gp score before initiation of steroid treatment was significantly associated with a positive response to treatment (P=0.01). These results indicate that lamina propria lymphocyte expression of p-gp is upregulated after prednisolone treatment in dogs with IBD, and that mucosal expression of p-gp may be of value in predicting the response to therapy.