Fish & Invertebrate Oncology

Question 1

Describe the common neoplasms of fish.

What species appear to get neoplasia more commonly?

What are some of the tumors that are unique to fish?

Answer 1

• Neoplasia
  
  • Cutaneous (esp papillomas), ocular, peripheral nerve, gonadal and renal tumors (esp nephroblastomas) are common in fish
  • Present as cutaneous mass, ocular mass, or coelomic distention
  • Benign >> malignant
  • Etiology
    
    • Depends on neoplasm
    • Retroviruses - walleye dermal sarcomas, salmon swim bladder leiomyosarcomas, damselfish neurofibromas
    • Herpesviruses
    • Adenoviruses - red seabream leukemia
    • Parasites -
      
      • Pseudobranch tumors/X cell disease in Atlantic cod
      • Plasmacytoid leukemia in salmonids assoc with microsporidians
      • Intestinal carcinomas in zebrafish with nematodes Pseudocapillaria
    • water/feed contaminants
    • Excessive UV, light, gamma exposure - retinal neoplasia from metal halide blue light in nocturnal pajama cardinal fish
    • Immersion meds - formalin, malachite green
  • Signalment - wild and captive, reported more in bony fish
    
    • Some spp seem prone to particular neoplasms
      
      • Fibromas or odontogenic hemartomas in FW angelfish
      • Melanomas in platies and swordtails
      • Ovarian neoplasms in adult intact female koi
      • Papillomas in sand tigers, guitarfish, and bamboo sharks
  • Findings
    
    • Usually individuals affected but epizootics have been reported ie ameloblastomas, in wild and cultured Chinook salom, renal papillary cystic adenomas and adenocarcinomas in oscars
    • Dermal nodules are often papillomas
    • Black masses are often melanomas, neurofibromas or fibromas
    • Ocular neoplasms are usually unilateral
  • Dx
    
    • Aspiration cytology of discrete masses
    • Incisional or excisional biopsies
    • Exploratory or endoscopic surgeries for internal masses
    • Cell categories are the same as in other vertebrates (round cell, epithelial cell, spindle cells, etc)
    • Benign vs malignant differentiation based on cell differentiation, rate of growth, local invasion and metastasis
    • Dx via histo, IHC for piscine markers or TEM for ultrastructure studies is often neded
  • Husbandry
    
    • If viral cause suspected, consider isolating the animal
  • Medical tx
    
    • Surgical debulking/removal. Can be curative, but margins can be difficult to achieve and recurrence is common.
    • Cryosurgery or cryotherapy - reported in goldfish, produced more scarring but less hemorrhage and lower recurrence rate compared to sx excision
    • Radiation reports rare
    • Chemo described in a few case reports ie local infiltration of carboplastin, cisplatin, 5-fluorouracil, cyclophosphamide, mitmycin C, bleomycin
  • Little info on prognosis for most fish neoplasms
• Neoplasia.
  
  • SCC – in mammals, hallmark feature are formation of keratin pearls, these are not observed in fish because keratinized epithelium is not present in most spp.
    
    • Exception is the chewing pad in the pharynx of some spp.
  • Tumors unique to fish.
    
    • Branchioblastomas – embryonic tumors of gill tissue.
    • Lepidocytomas – scale tumors.
    • Tumors of swim bladder gas gland.
    • Distant metastasis tends to be less common in fish
  • Chemical tumor induction
    
    • Carcinogens i.e. diethrylnitrosamine, N-methyl-AT-nitro-N’-nitrosoguanidine.
  • Association of tumors with infectious agents
    
    • Retroviruses
    • Herpesviruses
    • Papillomaviruses
    • Infestinal paratisism by Pseudocapillaria tomentosa
      
      • Hepatic or ductular tumors in zebrafish
    • Microsporidian infection
      
      • Granulosa cell hyperplasia/malignant ovarian tumor in long-jaw mudsucker
    • Appears to be species predispositions
      
      • Renal tubular neoplasms of Oscars
      • Nephroblastomas in Japanese eels
      • Testicular seminomas and ultimobranchial gland tumors in zebrafish.
      • Nerve sheath tumors gray snappers.
      • Gonadal stromal tumors in goldfish and carp.
      • Chromatophoromas in butterflyfish and Pacific rockfish.
      • Ameloblastomas in Chinook salmon.
      • Primitive neuroectodermal tumors in coho salmon.
      • Tendency for certain spp to develop certain tumors may be due to habitat and not genetics.
      • Hepatocellular neoplasms in English sole of Puget Sound, WA.
  • MYTH – idea that cartilaginous elasmobranchs do not develop cancer.
  • Round cell tumors.
    
    • Lymphocytic or lymphoblastic lymphomas and leukemias.
    • Plasmacytoid neoplasia in chinook salmon.
    • Histocytic tumors in northern pike.
  • Nodular lesions that are not actually tumors
    
    • Parasite induced granulomas or cysts
    • Protozoan induced ‘X-cell pseudotumors’
    • Viral-induced cellular hypertrophy
      
      • i.e. fibroblast enlargement caused by lymphocystis iridovirus.
    • Regenerative hyperplasia of the liver as a response to hepatotoxicants i.e. polycyclic aromatic hydrocarbons.