The progressive growth and spread of tumour cells in the form of metastases requires an interaction of healthy host cells, such as endothelial cells, fibroblasts, and other cells of mesenchymal origin with immune cells taking part in innate and adaptive responses within the tumour lesion and entire body. The host cells interact with tumour cells to create a dynamic tumour microenvironment, in which healthy cells can both positively and negatively influence the growth and spread of the tumour. The balance of cellular homeostasis and the effect of substances they secrete on the tumour microenvironment determine whether the tumour has a tendency to grow or disappear, and whether the cells remain within the lesion or are capable of metastasis to other regions of the body. Intercellular interactions also determine the tumour’s susceptibility to radiation or other types of cancer treatment. They may also be a rational explanation for differences in treatment outcomes, in which some metastases regress and others progress in response to the same treatment method.

Immunohistochemical studies have become an indispensable element of establishing the correct histopathological diagnosis of poorly differentiated lesions, proving particularly suitable, and occasionally indispensable, for diagnosis of poorly differentiated neoplastic tumours. Knowledge of the mechanism of action and normal reaction of individual proteins is required in selection of the antibody pattern for a given tissue and in evaluation of the obtained results. This paper aims to promote the application of immunohistochemical techniques in routine diagnosis, especially in cases of poorly differentiated or undifferentiated tumours.

OBJECTIVE To compare the orthogonal diameter (visual metric) method against a manual perimeter tracing (planimetry) method to measure volume of brain tumors in dogs by use of MRI scans. SAMPLE 22 sets of MRI brain scans pertaining to 22 client-owned dogs with histologically confirmed glioma. PROCEDURES MRI scans were reviewed by 2 operators, and scans revealing tumors with a degree of gadolinium enhancement that allowed discrimination between tumor tissue and healthy parenchyma were used. Each operator calculated tumor volume for each set of scans twice by use of visual metric and planimetry methods. Inter- and intraoperator variability were assessed by calculation of an agreement index (AI). RESULTS Mean ± SD intraoperator AIs were 0.79 ± 0.24 for the visual metric method and 0.89 ± 0.17 for the planimetry method. Intraoperator variability for both operators was significantly less when the planimetry method was used than when the visual metric method was used. No significant differences were identified in mean interoperator AI between visual metric (0.68 ± 0.28) and planimetry (0.67 ± 0.31) methods. CONCLUSIONS AND CLINICAL RELEVANCE The lower intraoperator variability achieved with the planimetry versus visual metric method should result in more precise volume assessments when the same operator performs multiple volume measurements of brain tumors in dogs. Equivocal results for interoperator variability may have been due to method variance or inadequate preliminary training. Additional studies are needed to evaluate the suitability of planimetry for assessing response to treatment.