A Collision Tumour Consisting of Malignant Trichoblastoma and Melanosarcoma in a Rabbit

Mast cell and plasma cell collision tumor in the spleen of a dog

“…independent neoplasms adjacent to each other at the same anatomic site . The coexistence often results in intermingling of cellular growth which is described as “collision” …”

“…Three case reports of collision tumors involved the skin (a hepatoid gland adenoma and a malignant melanoma; a hemangiosarcoma and a hepatoid cell/circumanal gland carcinoma; a malignant melanoma and an anaplastic sarcoma), one was associated with the testicle (a seminoma and a Sertoli cell tumor), and one was associated with the oral cavity of a dog (a squamous cell carcinoma and a malignant melanoma) were found . Case reports of collision tumors were found in a hamster, rabbit, and goat …”

“…[2][3][4][5] The coexistence often results in intermingling of cellular growth which is described as "collision". 6,7 In other articles, the definition of a collision tumor is described as 2 'histologically' distinct tumor types occurring at the same anatomic site; morphologically the tumors exhibit a "side-by-side" or "one upon another" pattern implying the diagnosis of collision tumor requires histologic evaluation. 8,9 Although some definitions imply a diagnosis of collision tumor requires histopathology, this case provides compelling support that in some instances a collision tumor can be diagnosed cytologically.…”

“…[2][3][4][5] A collision tumor should be differentiated from a composite/ complex or mixed tumor, which is a tumor arising from one cell type or clone that differentiates into 2 or more distinct cell lineages (eg, canine mammary carcinoma-complex type, canine mammary carcinoma-mixed type). 2,5,7,8,10 This is important since this may have an impact on patient management/treatment.…”

“…Case reports of collision tumors were found in a hamster, rabbit, and goat. 2,4,7 In human medicine, case reports of collision tumors are numerous and described in many anatomic locations (eg, gastrointestinal tract, liver, thyroid gland, adrenal gland, brain, skin, ovary, prostate, and lymph node). Interestingly, no case reports were found after a search for splenic collision tumors in people.…”