Hemic Neoplasia Research Articles

Unravelling epigenetic mechanisms in Cerastoderma edule genome: a comparison of healthy and neoplastic cockles

Cancer is a multifaceted genetic disease characterized by the acquisition of several essential hallmarks. Notably, certain cancers exhibit horizontal transmissibility, observed across mammalian species and diverse bivalves, the latter referred to as hemic neoplasia. Within this complex landscape, epigenetic mechanisms such as histone modifications and cytosine methylation emerge as fundamental contributors to the pathogenesis of these transmissible cancers. Our study delves into the epigenetic landscape of Cerastoderma edule, focusing on whole-genome methylation and hydroxymethylation profiles in heathy specimens and transmissible neoplasias by means of Nanopore long-read sequencing. Our results unveiled a global hypomethylation in the neoplastic specimens compared to their healthy counterparts, emphasizing the role of DNA methylation in these tumorigenic processes. Furthermore, we verified that intragenic CpG methylation positively correlated with gene expression, emphasizing its role in modulating transcription in healthy and neoplastic cockles, as also highlighted by some up-methylated oncogenic genes. Hydroxymethylation levels were significantly more elevated in the neoplastic samples, particularly within satellites and complex repeats, likely related to structural functions. Additionally, our analysis also revealed distinct methylation and activity patterns in retrotransposons, providing additional insights into bivalve neoplastic processes. Altogether, these findings contribute to understanding the epigenetic dynamics of bivalve neoplasias and shed light on the roles of DNA methylation and hydroxymethylation in tumorigenesis. Understanding these epigenetic alterations holds promise for advancing our broader understanding of cancer epigenetics.

Disseminated neoplasia in cultured hard clams (Mercenaria mercenaria).

Marine bivalves are commonly affected by disseminated neoplasia of presumed hemocytic origin (i.e., hemic neoplasia and hemocytic neoplasia). Histopathology of 520 cultured hard clams (Mercenaria mercenaria) from Florida was performed for health surveillance over a consecutive 13-month period. Disseminated neoplasia was identified in 9 of 520 animals (1.7%). The neoplasia was characterized by the presence of large, round to oval, anaplastic cells within hemolymphatic vessels and sinusoids with variable infiltration into adjacent connective tissues of the visceral mass, mantle, foot, and/or adductor muscles. Frequent involvement and/or infiltration of the gill was also identified (5/9). Disseminated neoplasia in other species of clams, mussels, and cockles is considered a transmissible disease. At this time, it is unknown if these hard clams represent de novo development of the disease or potential transmission; however, this report expands both the geographic and host range for this condition.

Mitochondrial genome sequencing of marine leukaemias reveals cancer contagion between clam species in the Seas of Southern Europe.

Clonally transmissible cancers are tumour lineages that are transmitted between individuals via the transfer of living cancer cells. In marine bivalves, leukaemia-like transmissible cancers, called hemic neoplasia (HN), have demonstrated the ability to infect individuals from different species. We performed whole-genome sequencing in eight warty venus clams that were diagnosed with HN, from two sampling points located more than 1000 nautical miles away in the Atlantic Ocean and the Mediterranean Sea Coasts of Spain. Mitochondrial genome sequencing analysis from neoplastic animals revealed the coexistence of haplotypes from two different clam species. Phylogenies estimated from mitochondrial and nuclear markers confirmed this leukaemia originated in striped venus clams and later transmitted to clams of the species warty venus, in which it survives as a contagious cancer. The analysis of mitochondrial and nuclear gene sequences supports all studied tumours belong to a single neoplastic lineage that spreads in the Seas of Southern Europe.

Evidence of horizontal transmission of the cancer-associated Steamer retrotransposon among ecological cohort bivalve species.

Bivalve specimens from legacy frozen tissue collections, and others freshly obtained, were surveyed for the presence of the Steamer long terminal repeat (LTR)-retrotransposon associated with disseminated hemic neoplasia of the soft-shelled clam Mya areneria. Of 22 species investigated using primers for the pol region, only Atlantic M. arenaria, Atlantic and North Sea razor clams Ensis directus, and Baltic clams Macoma balthica from the North Sea were found to possess copies of Steamer in their genomes. Notably, close relatives like Mya truncata and Siliqua patula did not exhibit evidence of Steamer. Amplified Steamer sequences were uniformly identical in all M. areneria specimens, and were highly variable across specimens of E. directus. Variation in the latter included nucleotide polymorphisms among and within individuals as well as length variation in 2 specimens corresponding to the deletion of a predicted stable hairpin structure. Results implicate Atlantic razor clams as the proximal source for horizontal transmission of Steamer among ecologically similar yet markedly distantly related bivalves. The consequences of cross-species transmission of the Steamer retrotransposon are unknown, and the finding of Steamer in 3 bivalve species suggests that further spread is possible.

Single Plex Branched DNA as an Alternative Assay to QuantifyP53-Like mRNA Levels in Softshell ClamMya arenariaHemocytes

Previous studies have shown that hemic neoplasia in softshell clams is related to the level of P53 -like mRNA in hemocytes. Traditionally, the p53-like mRNA level has been quantified using quantitative real-time RT-PCR (Q RT-PCR). However, this technique requires several steps that are sources of contamination and may result in a low accuracy of the analysis. The novel aspect of this study is that the p53-like mRNA level was quantified directly from a lysate of hemocytes without any RNA extraction or reverse transcription steps. This assay is based on branched DNA (bDNA) signal amplification technology and enables quantification of p53-like mRNA levels in as few as 2,500 hemocytes, with a coefficient of variation close to 6% (range, 2–12%). A significant correlation (R2= 0.99, P ≤0.01, n= 5) was found between the p53-like mRNA quantified directly from hemocytes without RNA extraction and from 1 µg total RNA extracted from hemocytes using the classic TRIzol protocol. To compare p53-like mRNA levels in hemocytes from diseased clams collected in North River (Prince Edward Island, Canada) and from healthy clams found in Havre aux Maisons at Magdalene Island (Quebec, Canada), the quantification of relative p53-like mRNA levels was performed using our single plex assay. Data showed a significantly (P ≤0.01, n= 5) high expression of p53-like in the hemocytes of clams collected from North River. Therefore, although Q RT-PCR remains the most widely used technique for the quantification of gene expression level, we believe that single plex using bDNA technology could represent a new generation of mRNA quantification tool, enabling a more efficient mollusc health management.

Extreme thrombocytosis in a young cat.

A 7-month-old unvaccinated domestic shorthair cat was presented with a history of inappetence and hypersalivation. Clinical examination revealed fever, gingivitis and oral ulceration. An initial blood sample revealed a severe leukopenia and neutropenia and a feline panleukopenia virus (FPV) titre of 1:640; a second titre 10 days later was 1:2,560. A feline calicivirus (FCV) titre was 1:320 and the initial clinical signs and laboratory findings were attributed to a coinfection with FPV and FCV. The cat was treated with interferon omega. A blood sample taken 10 days later revealed a severe thrombocytosis of 3,448 × 109/L (reference range 200–500 × 109/L) confirmed by blood smear examination. The platelet count on day 35 was 4,990 × 109/L. No bone marrow examination was carried out. Two differential diagnoses for an extreme thrombocytosis are a reactive thrombocytosis or essential thrombocythemia (ET). ET is a hemic neoplasia that causes a severe and persistent thrombocytosis, and is a diagnosis of exclusion. Reactive thrombocytosis is generally mild to moderate and of shorter duration than described here, but an excessive response could have been caused by infection. The influence of additional factors such as an initial thrombocytopenia, age and interferon treatment are not clear but can be speculated on. Although the exact pathophysiology in this case remains unclear, such high, persistent thrombocyte numbers have not been reported in cats in the absence of a neoplastic process.

Immunophenotyping of Mya arenaria neoplastic hemocytes using propidium iodide and a specific monoclonal antibody by flow cytometry

Disseminated neoplasia (DN) is a disorder referred to as hemic neoplasia (HN) in the soft-shell clam Mya arenaria. Traditionally, diagnosis is performed by hematocytology or histology. The intensity of the disease is generally given as the percentage of transformed neoplastic cells out of total number of hemocytes. Flow cytometry techniques have found a field of application in diagnosis of HN with analysis of ploidy. Hemocytes of the soft-shell clams with HN display tetraploid DNA content, as shown by propidium iodide staining. This feature makes difficult HN diagnosis in the soft-shell clam, especially for early stages of the condition, since the percentage of normal circulating cells undergoing mitosis, which also are tetraploid, remains unknown in molluscs. Use of specific monoclonal antibodies in a flow cytometry assay was foreseen as a way to overcome the difficulty. The purpose of this study was to develop a double staining protocol using propidium iodide for hemocyte cycle analysis and the MAb 1E10 for staining of HN cells. Our results showed a correlation between tetraploid and MAb 1E10-stained hemocytes in a single clam with moderate HN. This protocol offers some potential for further investigation of this cell disorder. However, a validation step will be necessary to confirm our preliminary results.

Identification of DeltaN Isoform and Polyadenylation Site Choice Variants in Molluscan p63/p73-Like Homologues

The p53 family of transcription factors has been implicated in many vertebrate cancers. Altered p53 and p73 protein expression observed in leukemic cells of molluscs suggests that these transcription factors might be involved in invertebrate cancers as well. Here, we fully characterize the mRNA of four novel p53-like variants in the bivalve molluscs Mytilus trossulus (bay mussel) and Mytilus edulis (blue mussel). These species, widely used for environmental assessment, develop a hemic neoplasia (leukemia) that is frequently fatal. The correlation between expression of p53 and its close relative p73 and onset of molluscan leukemia was documented previously. We report the sequences of two distinct and novel p63/p73-like mRNAs, amplified by polymerase chain reaction (PCR) from both species. One of the p63/p73-like isoforms contains a 360 nt truncation in the 5' coding region. Based on this truncation and concomitant lack of a transactivation (TA) domain, we designate this variant as a DeltaNp63/p73-like isoform: the first to be reported in an invertebrate species. In mammalian species, DeltaNp73 potently inhibits the tumor-suppressive function of p73 and p53, and its overexpression serves as a robust marker for mammalian cancer. In addition, we report on the occurrence of alternate polyadenylation sites in the molluscan p63/p73: one proximal and one distal site, which differ by 1260 nt. We hypothesize that differential expression of various molluscan p63/p73-like isoforms, controlled in part by polyadenylation site choice variation, may help to interpret the apparently opposing roles of this gene in the development of cancer. Overall, this research further illustrates the utility of the molluscan model for studies involving the molecular mechanisms of oncogenesis in naturally occurring populations. The data presented here require a revisiting of hypotheses regarding evolution of the p53 gene family. Current hypotheses indicate that (1) the protostome gene family does not contain an intronic promoter for DeltaN expression and (2) p53 gene duplication did not occur in protostomes. Our characterization of DeltaN p63/73 in mussel suggests that molluscan p53 gene family members have acquired an intronic promoter or splicing mechanism, either by invention that predates the evolutionary split of deuterostomes from protostomes, or by parallel evolution. Our data also show that Mytilus p53, p63/p73, and DeltaNp63/p73 are identical in their core regions with variation limited to their C- and N-terminals, supporting the notion that alternative splicing, intronic promoter usage, and polyadenylation site choice may lead to expression of distinct isoforms originating from one common gene.

Biomarkers of environmental contaminants in field population of green mussel (Perna viridis) from Karnataka–Kerala coast (South West coast of India)

The green mussel Perna viridis was sampled from relatively clean and contaminated sites along the Kartanata-Kerala coast (south west coast of India) to study the tissue concentration of trace metals and biological responses to stress (biomarkers) such as sister chromatid exchange (SCE), chromosomal aberration, micronucleus (MN) test, hemic neoplasia (HN), Chromotest (Ames test) and comet assay. In general, mean tissue concentrations of toxic trace metals collected from 25 sampling sites were found to be below the World Health Organisation (WHO) permissible concentration given for seafood. The digestive gland extract of mussels from all 25 sampling sites showed negative reaction for mutagenic activity (Ames test) in the absence of metabolic activation. Very low levels of chromosomal aberration, SCE, MN, HN and comet cells were observed in mussels collected from both the urban associated and relatively clean sites. This study seems to indicate that that the coastal waters of Karnataka and Kerala are minimally contaminated with genotoxic and carcinogenic chemicals.

Flow cytometric patterns in blood from dogs with non‐neoplastic and neoplastic hematologic diseases using double labeling for CD18 and CD45

In dogs, flow cytometry is used in the phenotyping of immunologic cells and in the diagnosis of hemic neoplasia. However, the paucity of specific antibodies for myeloid cells and B lymphocytes and of labeled antibodies for multicolor techniques limits the ability to detect all leukocyte subpopulations. This is especially true for neoplastic and precursor cells. CD18 and CD45 are expressed on all leukocytes and are involved in cell activation, and together could be useful in helping determine cell lineage. The purpose of this study was to double label canine blood for CD18 and CD45 and to use the differential expression of antigens to identify leukocyte populations in dogs with non-neoplastic and neoplastic hematologic diseases. A template was developed using blood samples from 10 clinically healthy dogs and a back-gating technique. Differential leukocyte counts obtained with the template were compared with those obtained by manual and automated methods on blood samples from 17 additional healthy dogs. Blood samples obtained from 9 dogs with non-neoplastic (reactive) hematologic diseases and 27 dogs with hemic neoplasia were double stained for CD18 and CD45 using mouse anticanine CD18 monoclonal antibody (mAb) plus phycoerythrin-conjugated rat anticanine CD45 mAb and fluorescein isothiocyanate-conjugated rabbit antimouse IgG. Hemic neoplasms were diagnosed by cell morphology, and immunophenotypic and cytochemical markers. With the double label, neutrophils, eosinophils, monocytes, and T- and B-lymphocytes were identified. In reactive disorders, a population of activated neutrophils with high CD45 and CD18 expression was detected. In hemic neoplasia, cell lineage was easily determined, even in acute leukemia. Double labeling for CD18/CD45 may be useful as a screening method to evaluate hematologic diseases and help determine cell lineage, and to aid in the selection of a panel of antibodies that would be useful for further analysis.

Disseminated neoplasia in blue mussels, Mytilus galloprovincialis, from the Black Sea, Romania

Disseminated neoplasia, also called leukemia or hemic neoplasia, has been detected in 15 species of marine bivalve mollusks worldwide. The disease is characterized by the presence of single anaplastic cells with enlarged nuclei and sometimes frequent mitosis, in hemolymph vessels and sinuses. The neoplastic cells gradually replace normal hemocytes leading to the increased mortality of animals. The neoplasia reaches epizootic prevalences in blue mussels, Mytilus trossulus, in some areas, whereas prevalences in Mytilus edulis are generally very low. Mytilus galloprovincialis was suggested to be resistant to the disease although very low prevalences were documented from Spain in the Atlantic Ocean and Italy in the Mediterranean Sea. A case of disseminated neoplasia was discovered in M. galloprovincialis from among 200 specimens studied from the coast of the Romanian Black Sea. Histological preparation revealed the presence of large anaplastic cells with lobed nuclei. This observation extends the geographic range of marine bivalve mollusks with disseminated neoplasia to include the Black Sea.

Pilot study of the Olympia oyster Ostrea conchaphila in the San Francisco Bay estuary: description and distribution of diseases

Olympia oysters Ostrea conchaphila have declined markedly during the last century and are a focus of restoration in many embayments, including the San Francisco Bay (SFB) estuary. Oysters were collected from 17 sites in this estuary and nearby Tomales Bay in an effort to characterize diseases that may impact recovery of this species and captive rearing programs. Three diseases/disease agents including a Mikrocytos-like protist (microcell), a haplosporidian and hemic neoplasia were observed from several sites along the western margins of the SFB estuary suggesting a geographic localization of disease presence. Based on fluoresecent in situ hybridization (FISH) assays, the microcell is distinct from M. mackini and Bonamia spp. These data highlight the need for further elucidation of the haplosporidian and for careful health management of a declining species destined for captive rearing and supplementation.

Assessment of seasonal variability of cytochemical responses to contaminant exposure in the blue mussel Mytilus edulis (complex).

A selected suite of cytochemical parameters in Mytilus edulis are altered in response to field and laboratory exposure to chemical contaminants. These biomarkers include lysosomal stability, nicotinamide adenine dinucleotide phosphate (NADPH)-ferrihemoprotein reductase activity, liposfuscin deposition, and accumulation of lysosomal and cytoplasmic unsaturated neutral lipid. Normal variations in physiological processes (influenced by exogenous seasonal changes in temperature, salinity, food availability, etc.) may alter the sensitivity of these biomarkers to contaminant exposure. To address this issue, M. edulis (complex) were sampled monthly from a reference nonurban site (Coupeville, Penn Cove) and a polluted urban site (Seacrest, Elliott Bay) in Puget Sound, WA, for a period of 15 months. Physiological measurements including total length, total weight, somatic and mantle weights (an indication of gonadal development and reproductive status), condition index, and the presence or absence of hemic neoplasia (HN, or leukemia) were recorded. Significant differences in lysosomal stability, lysosomal and cytoplasmic unsaturated neutral lipids, lipofuscin deposition, and NADPH-ferrihemoprotein reductase activity in cells of the digestive gland or digestive tubules were generally found in mussels taken throughout the year from Seacrest compared to mussels sampled from Coupeville, consistent with exposure to chemical contaminants. No seasonally influenced suppression of the entire suite of parameters as measures of contaminant exposure was evident. Therefore these biomarkers can be used to evaluate contaminant exposure in mussels throughout the entire year.

Two epizootic diseases in Chesapeake Bay commercial clams, Mya arenaria and Tagelus plebeius.

Declining Chesapeake Bay harvests of softshell clams, together with historical and emerging reports of epizootic diseases in Mya arenaria, prompted a survey in summer 2000 of the health status of selected commercial clam populations. All sampled populations (8 M arenaria softshell clam, 2 Tagelus plebeius razor clam) were infected by Perkinsus sp. protozoans at prevalences ranging from 30 to 100% of sampled clams. Nucleotide sequences for the internal transcribed spacer (ITS) region of the rRNA gene complex were determined for clonal in vitro Perkinsus sp. isolates propagated from both M. arenaria and T plebeius. Multiple polymorphic sequences were amplified from each isolate, but phylogenetic analysis placed all sequences into 2 clades of a monophyletic group, which included both recently described clam parasites P. chesapeaki and P. andrewsi. Sequences amplified from each clonal isolate were found in both sister clades, one containing P. andrewsi and the other P. chesapeaki. Most (7 of 8) M. arenaria samples were also affected with disseminated neoplasia (DN), at prevalences of 3 to 37%, but neither T. plebeius sample showed DN disease. Disease mortalities projected for sampled clam populations, especially those affected by both diseases, may further deplete subtidal commercial clam populations in mesohaline portions of Chesapeake Bay.

Environmental Contaminants and the Prevalence of Hemic Neoplasia (Leukemia) in the Common Mussel (Mytilus edulisComplex) from Puget Sound, Washington, U.S.A.

The relationship between hemic neoplasia, a blood cell disorder in bivalve molluscs, and chemical contaminants was evaluated in the common mussel (Mytilus eduliscomplex). Hemic neoplasia (HN) is endemic to mussel populations in Puget Sound. The prevalence of hemic neoplasia ranged from 0 to 30% in mussels from nine sites in Puget Sound, Washington. Organic chemical contamination in sediment from these sites range from 0.1 to 64.0 ppm of polycyclic aromatic hydrocarbons (PAHs) and 0.07 to 0.50 ppm chlorinated hydrocarbons. No relationship between the body burden of environmental contaminants and the prevalence of HN in mussels was identified. To evaluate the short-term ability of chemical contaminants to induce HN in mussels, mussels, from a site where mussels were previously determined to be HN free, were fed microencapsulated PAHs (composed of a mixture of phenanthrene, flouranthene, and benzo[a]pyrene) or PCBs (Aroclor 1254) and the prevalence of HN was assessed after 30 days of exposure. Although an apparent increase in HN prevalence (20 to 30%) was observed in all treatments groups except the untreated controls, no significant difference in the prevalence of HN was observed between the control group of mussels fed corn oil (vehicle) and mussels fed either PAHs or PCBs in corn oil. A long-term (180-day) exposure study was conducted to evaluate the influence of PAHs or PCBs in modulating the prevalence of HN in a mussel population already exhibiting a moderate HN prevalence. Mussels, from a site where mussels were previously determined to exhibit a background prevalence of HN, fed microencapsulated PAHs, PCBs, and corn oil (vehicle) over a long time period (180 days), revealed an apparent increased prevalence of HN (30 to 40%) above the low levels (20%) initially present. However, no significant difference in the prevalence of HN was observed between the control group of mussels fed corn oil (vehicle) and mussels fed either PAHs or PCBs in corn oil. Although chemical contaminants have been proposed as a modulating factor in the development and promotion of HN in bivalve molluscs from environmentally stressed and degraded habitats, we find no evidence that chemical contaminants induce or promote the development of HN in the musselM. eduliscomplex.

Thrombocytopenia associated with neoplasia in dogs.

Ten percent (214/2,059) of all dogs with cancer at North Carolina State University Veterinary Teaching Hospital had thrombocytopenia. The thrombocytopenia was associated with infectious/inflammatory etiologies in 4%, miscellaneous disorders (therapy, bone marrow failure, disseminated intravascular coagulation) in 35%, and neoplasia without identifiable secondary factors in 61% of cancer-bearing dogs. Classifying these dogs by tumor groups revealed the following proportionate ratios: lymphoid, 29%; carcinoma, 28%; sarcoma, 20%; hemic neoplasia, 7%; multiple, 5%; unclassified, 3%; benign, 3%; brain, 3%; and endocrine, 3%. Dogs with hemangiosarcoma, lymphoma, and melanoma were at increased risk of developing thrombocytopenia. Cytotoxic therapy was the major factor increasing the risk of thrombocytopenia in dogs with melanoma. Golden Retrievers were the only breed recognized with a predisposition to develop thrombocytopenia. If thrombocytopenia is identified in a dog with cancer, we recommend thorough evaluation of the coagulation system before surgery or therapy, and careful consideration of the risks and potential benefits of myelosuppressive or L-asparaginase therapy.

Histopathological progression of hemic neoplasms in the tropical crab Paratelphusa hydrodromous (Herbst) treated with sublethal cadmium chloride

Tropical crab Paratelphusa hydrodromous were exposed in the laboratory to five sublethal cadmium chloride concentrations (0.02, 0.05, 0.25 and 0.50μM/L) for 30 days to evaluate the cellular inflammatory and chronic pathologic responses. The most frequent pathologic responses of hepatopancreas exposed to 0.25–0.50 μM CdCl2/L were atrophy of R-cells and the development of granulomatous reaction consisting of granulocytes and monomorphic basophilic cells. Coagulative necrosis was evident in the young oocytes at 0.05 μM CdCl2/L which was accompanied by the increased vitellophagia of follicle cells. Thirty-day exposure to 0.25–0.50 μM CdCl2/L shortened the reproductive life span of the crabs by inducing spontaneous atresia and granulocytosis. Eosinophilic granulocytes, the most numerous cell type found in the necrotic centers, phagocytosed the masses of cellular debris and yolk from cadmium-induced atretic oocytes. The widespread proliferation of basophilic cells related to hyalinocyte with high nucleocytoplasmic ratio would suggest the development of hemic neoplasia. Heavy granulocytic infiltration was the typical cellular inflammatory response during chronic pathological conditions.

Alternate pathogenesis of systemic neoplasia in the bivalve mollusc Mytilus

The proliferative disease systemic neoplasia, also termed hemic neoplasia or disseminated sarcoma, was studied in four Puget Sound, Washington populations of the bay mussel ( Mytilus sp.). Using flow cytometric measurement of DAPI-stained cells withdrawn from the hemolymph, DNA content frequency histograms were generated for 73 individuals affected by the disease. The cells manifesting systemic neoplasia were found to exist as either of two separate types, characterized by G 0G 1 phase nuclear DNA contents of either approximately 4.9× haploid (pentaploid form) or approximately 3.8× haploid (tetraploid form). The two disease forms were found to coexist in all four mussel populations sampled, with overall relative prevalences of 66% pentaploid form, 29% tetraploid form, and 5% exhibiting both disease forms simultaneously. These findings represent the first unequivocal demonstration of multiple cell types in a bivalve neoplasia. The two forms appear to represent separate pathogenetic processes rather than sequential stages of a single pathogenesis. Two cell cycling parameters associated with proliferative activity were employed to compare the alternate forms: (i) the percentage of cells assigned to the DNA Synthesis (S) phase of the neoplastic cell cycle, and (ii) the proportion of neoplastic cell mitotic figures in hemocytological preparations. Mean values for both parameters were significantly higher for mussels with the tetraploid form of the disease, suggesting a higher rate of proliferation relative to the pentaploid form. Qualitatively, cells of the tetraploid form contained slightly lower nuclear and cytoplasmic volumes compared to those of the pentaploid form. An observed wide variation in neoplastic cell nuclear size within either disease form may reflect the distribution of cells in the G 0G 1, S, and G 2M phases of the cell cycle. Potential etiologic relationships between the two forms are discussed.

Failure of transmission of hemic neoplasia of bay mussels, Mytilus trossulus, to other bivalve species

Failure of transmission of hemic neoplasia of bay mussels, Mytilus trossulus, to other bivalve species

Progressive development of circulating polyploid cells in Mytilus with hemic neoplasia

Progressive development of circulating polyploid cells in Mytilus with hemic neoplasia