"Histologic Interpretation" TUMOR TIDBITS, A BIWEEKLY EMAIL NEWSLETTER FROM GULF COAST VETERINARY ONCOLOGY Number 87; February 7, 2003. ======================================================================= THIS WEEK'S TUMOR TIDBIT: Histologic Interpretation ======================================================================= ANNOUNCEMENTS March 15th is our Second Annual Patient Celebration in Houston. March 4th we begin offering 3 day per week service in San Antonio. April 1st we begin a clinical trial for anemia with free cancer services in both locations. Visit our web site for other exciting information. ======================================================================= Is histopathology an exact science? This Tidbit discusses our approach to interpreting histopathologic reports. For prognostic purposes, it is important to know whether a tumor is benign or malignant. The histopathological cellular criteria for malignancy are similar to the criteria used in cytological evaluation; however, histopathology allows for examination of the neoplasm's architecture and growth pattern (invasiveness). Malignant tumors often exhibit marked pleomorphism. Numerous and abnormal mitotic figures are often scattered throughout the tissue section. Cell cohesiveness and cell-to-cell contact are decreased, and there is an increased tendency for cells to migrate away from their site of origin. Malignant cells often invade the surrounding tissues, lymphatics, and blood vessels. It is this process of invasion that leads to metastasis, which is the hallmark of malignancy. In addition to providing a diagnosis, histopathological examination can frequently be used to provide important prognostic information. The histopathological grade of a tumor may predict clinical behavior. Low-grade malignancies frequently are slowly progressive and may be treated by local therapy such as surgery. High-grade malignancies are frequently invasive, rapidly growing, and metastatic in their behavior. Histopathological grading is generally determined by criteria of tumor differentiation, mitotic index, necrosis, and blood vessel invasion. For example, histopathological grading of canine mast cell tumors has prognostic significance and is based on the degree of differentiation of the individual cells. The more differentiated a mast cell is, the better the prognosis. In a study of dogs with mast cell tumors, 6 per cent with undifferentiated tumors were alive at 15 months, 44 per cent with moderately differentiated (intermediate grade) mast cells were alive at 15 months, and 83 per cent with well-differentiated tumors were alive 15 months after their diagnosis. Criteria for histopathological grading have been defined for several other tumor types, including canine lymphoma and canine mammary carcinoma. Mitotic index is of prognostic significance in canine soft-tissue sarcomas. In one study of sarcomas in dogs, tumors with a mitotic index of nine or more mitotic figures at a magnification of 400, the median survival time was 49 weeks and recurrence rate of 62 per cent was observed, whereas tumors with a mitotic index of less than nine mitotic figures at the same magnification had a median survival time of 118 weeks and a recurrence rate of only 25 per cent. Microscopic examination of cut margins of tissue is a common way to determine if a tumor has been completely excised. The presence of neoplastic cells at a surgical margin can influence the decision about the need for further surgery or adjunctive therapy such as radiation or chemotherapy. If no neoplastic cells are visible at the margins of the biopsy specimen, clinicians usually assume that the excision is complete. Incomplete excision is assumed if neoplastic cells extend to the biopsy margin. The report of "clean" surgical margins may provide a misleading interpretation of the completeness of surgical excision. It is important to remember that pathologists examine only a small section of tissue relative to the volume excised. To conclude that all margins are free of neoplastic infiltration based on the evaluation of a 5- to 6-mm slice of a portion of the tumor may lead to an erroneous conclusion. It is easy to understand how false interpretations can occur with excision of tumors that spread irregularly along fascial planes or that have small clusters of neoplastic cells invading surrounding tissues. Examination of different tissue planes of a biopsy specimen can lead to different conclusions about the completeness of the surgical excision. A false report of a clean surgical margin would likely delay appropriate additional therapy and have a negative influence on the outcome of any therapy. Inaccurate histopathology reports can also result from inflamed tumors. Inflammation can obscure the true tumor morphology, causing the pathologist to render an inaccurate diagnosis. A knowledge of the biological behavior of a tumor coupled with high-quality specimen submission is the most useful approach to determine the need for additional therapy. AT GULF COAST VETERINARY ONCOLOGY It is understandable, when attempting to spare client expenses, that a “mini-“ histopathology report be requested following an incisional or excisional biopsy. We prefer, on initial oncologic consultation, to examine a complete microscopic description along with interpretation on every histopathology report. This allows us the insight to predict biological behavior of the tumor and to provide a prognosis or treatment plan that is most appropriate for that pet and for that family. In some instances, the microscopic description (objective information) does not make the pathologists interpretation (often considered the diagnosis). In those circumstances, it is very appropriate to call the original pathologist to provide any helpful information that might clarify what, if any, additional diagnostics may be needed to confirm the pet’s final diagnosis or prognosis (immunohistochemistry, imaging, etc). ======================================================================= As always, we hope this info helps and don't hesitate to call or email us Gulf Coast Veterinary Oncology! Kevin A. Hahn, DVM, PhD, Diplomate ACVIM (Oncology), drhahn@gcvs.com Janet K. Carreras, VMD, Diplomate ACVIM (Oncology), drcarreras@gcvs.com Glen K. King, DVM, MS, Diplomate ACVR (Radiology & Radiation Therapy), drking@gcvs.com Gulf Coast Veterinary Diagnostic Imaging & Oncology 1111 West Loop South, Suite 150, Houston, TX 77027 P: 713.693.1166 F: 713.693.1167 W: www.gcvs.com