Haemic neoplasia in soft-shell clams (Mya arenaria): recent outbreaks in Atlantic Canada and discovery of a p53 gene homologue associated with the condition

In 1999, examination of soft-shell clam (Mya arenaria) mortalities at an experimental lease on Prince Edward Island (PEI) revealed a 95% prevalence of advanced haemic neoplasia (leukaemia). Low prevalences of this condition had been documented previously in soft-shell clams from Nova Scotia and the Bay of Fundy, as well as the southern Gulf of St. Lawrence, but this was the first recorded case of mortalities in Atlantic Canada associated with the condition. An intensive survey of PEI clam beds revealed that both negative and positive sites for haemic neoplasia are linked to seed transfers as well as proximity to agriculture activity. An independent study investigating a similar condition in relation to industrial pollutants (e.g., PCBs) found high levels of leukaemia in clams collected from Sydney Mines, NS, Kitimat Arm, BC, as well as sites along the east coast of the United States with high levels of anthropogenic substances. In an attempt to identify the role of industrial chemicals in inducing this condition, research focused on the detection of a gene resembling the p53 gene family in leukaemic clams. A similar gene has also been discovered in bar clams (Spisula solidissima). These findings suggest that clams may be ideal models for studying mechanisms of disease induced by chemical contaminants. Such molecular links to chemical exposure may have profound implications for many animals, including humans, and may prove useful for focusing on the triggers of neoplasia in clams from among the many possibilities (viral, genetic, environmental and anthropogenic).