The low incidence of reported tumours in elasmo-branchs has led to the assumption that the group
rarely develops cancerous diseases (Loprinzi et al. 2005). This, combined with some studies reporting
a therapeutic benefit in cartilage extract (e.g. Cho & Kim 2002), has resulted in a worldwide demand
for shark cartilage products for use as alternative therapies (Berzins & Hovland 1999). This demand
has, at least in part, increased the pressure on shark populations contributing to their worldwide decline
(Ostrander et al. 2004). While reported cases are relatively low, both benign and cancerous prolifera-
tive lesions have been reported in 21 species of sharks from over 9 families (Ostrander et al. 2004; National Cancer Institute 2007).