"Collision tumors" consist of two independent but coexisting tumors. This uncommon situation might be easily mistaken for a composite tumor where one histogenetic event originates from two apparently distinct neoplasms. Colorectal collisions are particularly unusual; here, we report the exceedingly rare case of a 61-year-old man with malignant melanoma and adenocarcinoma colliding in the rectum. Collision tumors have an idiopathic pathophysiology and in fact "accidental meeting" is accepted by many authors. This article discusses the concepts about cancer development, which are overlooked by this hypothesis, another theory to explain that this rare occurrence involves microenvironment changes.

Dipyrone (metamizole) is well-known for its powerful effect with central and peripheral activity. This meta-analysis involved articles published between 1973 and 2021, revealing that Brazil is the country which most published scientific articles relating the use of dipyrone in dogs, and this drug is widely recommended as an analgesic to control pain in cases of postoperative and cancer. Dipyrone is one of the favorite drugs used in small animal clinic in Brazil, and 12 commercial brands are available to use in dogs at doses among 25 to 50mg/kg for oral, intravenous and intramuscular administration. The effects of dipyrone may be potentiated when used in combination with other analgesic agents such as tramadol. In several studies, the occurrence of vomiting has been observed as an adverse effect, especially when the drug is used during surgical procedures, but metamizole has presented a low potential to cause gastric ulceration. The meta-analysis study of the use of dipyrone in dogs shows the clinical importance of this drug in Brazil, being an effective and safe medication, as long as it is used in the indicated dose of 25 mg/kg.

Little is known about the toxicity of immune modulators in fish. Zafirlukast is an anti-inflammatory that antagonizes cysteine leukotriene receptors (CysLTR1). Aiming to study immunomodulatory treatments on fish health, this study evaluated the clinical safety of oral zafirlukast treatment, through biochemical and hematological analyzes during acute inflammatory reaction in Nile tilapia (Oreochromis niloticus), induced by Aeromonas hydrophila bacterins. 72 young tilapias were randomly divided in 9 aquariums (100 L each, n=8) to compose the following treatments: T0 (control), T1 (Treatment with 250 µg zafirlukast) and T2 (Treatment with 500 µg zafirlukast). Eight animals were evaluated per treatment in three periods: six, 24 and 48 hours post-inoculation (HPI), blood collection was performed for hematological and serum biochemical evaluation. The study of hepatic and renal functionality revealed that treatment with both doses of zafirlukast did not result in changes in the circulating values of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase, creatinine, triglycerides, cholesterol, and total protein, suggesting that the drug has not presented hepatotoxicity, as well as compromised liver and kidney functions. Tilapia submitted to treatment with 500 µg showed adverse hematological effects characterized by polycythemia associated with microcytosis. Therefore, oral treatment with zafirlukast has demonstrated clinical safety at a therapeutic dose of 250 µg in tilapia during acute aerocystitis, although hematological changes were observed in tilapia treated with overdose of this leukotriene blocker.