In the peritoneal cavity, invasion of fat or of organ walls is again the most reliable indicator of malignancy, but entrapment of benign cells in organizing granulation tissue or between fat lobules is frequent and confusing. Proliferations confined to the pleural or peritoneal space, particularly linear arrays of atypical mesothelial cells on the free surface, should not be called malignant in the absence of unequivocal invasion. Cytologic atypia is often not helpful in separating benign from malignant reactions, because benign processes are commonly atypical and mesotheliomas are often deceptively monotonous. Densely packed mesothelial cells within the pleural space are frequent in benign reactions, but densely packed mesothelial cells within the stroma favor a diagnosis of malignancy. Elongated capillaries perpendicular to the pleural surface are seen in organizing effusions but are not a feature of sarcomatous mesotheliomas.
Necrosis is usually a sign of malignancy but is occasionally seen in benign mesothelial reactions.
Keratin staining is useful in indicating the distribution of mesothelial cells, and particularly in demonstrating penetration of mesothelial cells into the stroma or adjacent structures, but is of no help in separating benign and malignant proliferations because both are keratin-positive. Although both p53 and EMA staining have been proposed as markers of mesothelial malignancy, in our experience they are not helpful for the individual case. No significant toxicities, infection of patient contacts, or tumor regressions were observed. This suggests that VV may be a good vector for repeated cytokine gene therapy of solid human cancer. Although the search strategy has been refined as best as possible, citations may appear that are not directly related to the topic, and occasionally relevant references may be omitted.