In a literature review, Geraci et al. (1987) stated that there were only 41 confirmable tumors reported in cetaceans, 14 of which being reported by themselves. One of those tumors was from the St. Lawrence, a transitional cell carcinoma reported in a beluga whale (Delphinapterus leucas) from Martineau et al. 1985. Since then, many severe pathological lesions including neoplasms have been reported in that small, isolated and highly contaminated population of beluga whales, and are herein discussed.

Six malignant tumors, ten benign tumors, and three abdominal masses (probable neoplasms that could not be confirmed histopathologically) were observed in 24 beluga whales necropsied between 1988 and 1990. There were more than one tumor in four animals: two malignant tumors (mammary gland adenocarcinoma and hepatocellular carcinoma) and one benign tumor (pulmonary chondroma) in a 22+ year old female (9­88); one malignant tumor (intestinal adenocarcinoma) and one benign tumor (papilloma of the first gastric compartment) in a 29+ year old male (7-89) and a 20+ year old male (8-89); a malignant tumor (thymic lymphosarcoma) and a benign tumor (papilloma of the first gastric compartment) in an 18+ year old male (1-90). Overall, eleven animals out of 24 (46%) had at least one tumor. The rate of incidence of malignant tumors was five animals out of 24 (21 %); that of benign tumors was ten animals out of 24 (42%). Only one type of malignant neoplasm, an intestinal adenocarcinoma, occurred more than once (7-89 et 8-89). One or more papillomas of the first gastric compartment, which are benign tumors, were present in eight animals. Individuals with malignant tumors were aged between 18+ and 29+ year; those with benign tumors were between 14 and 29+ years old; none of these animal was emaciated.

Animals without tumors were two juveniles (aged 1,5 and 3,5 years) and twelve adults aged 13 to 27 years old. Overall, 23 tumors have been reported in 45 beluga whales from the same population that were necropsied since 1982 (Table 1). Tumors were not observed in 4 carcasses of Atlantic white-sided dolphins (Lagenorhyncus acutus), 2 carcasses of harbour porpoises (Phocoena phocoena), and 15 carcasses of three species of seals (Phoca vitulina, Pagophilus groenlandicus, Halichoerus grypus) from the same waters.

Only 4 tumors have been reported in cetaceans from other locations since the publication of Geraci et al. (Table 2). Overall, 23 of the total of 67 tumors reported in cetaceans (34%) were found in the same small population (around 500 animals) beluga whales, in which high levels of organochlorines and heavy metals have been demonstrated (Martineau et al. 1987, Muir et al. 1990, Wagemann et al. 1990). This would suggest an influence of carcinogenic compound(s), or a decreased resistance to the development of tumors in the animals of this population.

Table 1. Tumors in St Lawrence beluga whales

Table 2: Tumors in cetaceans other than St. Lawrence beluga whales and not cited by Geraci et al.

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