A pilot study of cabergoline for the treatment of metastatic breast cancer.

PURPOSE: The prolactin (PRL) receptor is over-expressed in breast cancer, and pre-clinical data indicate that it contributes to breast oncogenesis. Cabergoline is a potent dopamine receptor agonist of D2 receptors and has a direct inhibitory effect on pituitary PRL secretion. METHODS: A phase II study of cabergoline in patients with metastatic breast cancer was conducted. The primary end point of the study was to determine the clinical benefit rate (CBR) at 2 months. Eligible patients had tumors of any receptor status with no limit of prior lines of therapy. Measurable and unmeasurable diseases were allowed. Cabergoline 1 mg orally, twice weekly (1 cycle = 4 weeks) was given until disease progression or unacceptable toxicity. PRL receptor immunohistochemical staining was performed on available baseline tumor tissue; serial serum PRL levels were assessed. RESULTS: Twenty women were enrolled; 18 were evaluable for CBR. Tumor receptor status was distributed as follows: HR-any/HER2+ 2(10%), HR+/HER2- 18 (90%). The CBR was 33% (6/18), median progression free survival was 1.8 months, and median overall survival was 10.4 months. Two patients experienced disease control for over 12 months. Most common treatment-related adverse events were nausea (30%), fatigue (25%), and elevation in alkaline phosphatase (15%). Nine patients had baseline tissue for analysis; there was no association between baseline tumor PRL receptor expression and clinical benefit (p = 0.24). Change in serum PRL level and response were not correlated after 2 months of treatment (p = 0.64). CONCLUSION: Cabergoline was well tolerated, and while the ORR was low, a small subset of patients experienced extended disease control.

Requirement of nuclear prolactin for interleukin-2--stimulated proliferation of T lymphocytes.

Prolactin (PRL) is necessary for the proliferation of cloned T lymphocytes in response to interleukin-2 (IL-2). Translocation of PRL into the nucleus occurs during IL-2--stimulated mitogenesis. Therefore, the function of intranuclear PRL in T cell proliferation was tested. Eukaryotic expression vectors were prepared to express wild-type PRL [PRL(WT)], PRL that lacks the signal sequence for translocation into the endoplasmic reticulum [PRL(ER-)], and chimeric PRL in which the signal peptide was replaced with the sequence that directs the nuclear translocation of the SV40 large T antigen [PRL(NT+)]. Expression of these constructs in a T cell line (Nb2) responsive to PRL and IL-2 resulted in localization of PRL in the extracellular milieu, cytoplasm, or nucleus, respectively. Stimulation with IL-2 alone resulted in a five- to tenfold increase in the incorporation of [3H]thymidine by cells expressing PRL(NT+) or PRL(WT) as compared to PRL(ER-) or the parental Nb2 cells. Only the PRL(NT+) clone proliferated continuously with IL-2 stimulation in the presence of antiserum to PRL. These results demonstrate that nuclear PRL is necessary for IL-2--stimulated proliferation and suggest that a peptide hormone can function in the nucleus without binding to its cell surface receptor.

Nek3 kinase regulates prolactin-mediated cytoskeletal reorganization and motility of breast cancer cells.

Prolactin (PRL) stimulates the cytoskeletal re-organization and motility of breast cancer cells. During PRL receptor signaling, Vav2 becomes phosphorylated and activated, an event regulated by the serine/threonine kinase Nek3. Given the regulatory role of Vav2, the function of Nek3 in PRL-mediated motility and invasion was examined. Overexpression of Nek3 in Chinese hamster ovary transfectants potentiated cytoskeletal re-organization in response to PRL. In contrast, downregulation of Nek3 expression by small-interfering RNA (siRNA) attenuated PRL-mediated cytoskeletal reorganization, activation of GTPase Rac1, cell migration and invasion of T47D cells. In addition, PRL stimulation induced an interaction between Nek3 and paxillin and significantly increased paxillin serine phosphorylation, whereas Nek3 siRNA-transfected cells showed a marked reduction in paxillin phosphorylation. Analysis of breast tissue microarrays also demonstrated a significant up-regulation of Nek3 expression in malignant versus normal specimens. These data suggest that Nek3 contributes to PRL-mediated breast cancer motility through mechanisms involving Rac1 activation and paxillin phosphorylation.

Stabilization of prolactin receptor in breast cancer cells.

The role of the hormone prolactin (PRL) in the pathogenesis of breast cancer is mediated by its cognate receptor (PRLr). Ubiquitin-dependent degradation of the PRLr that negatively regulates PRL signaling is triggered by PRL-mediated phosphorylation of PRLr on Ser349 followed by the recruitment of the beta-transducin repeats-containing protein (beta-TrCP) ubiquitin-protein isopeptide ligase. We report here for the first time that interaction between PRLr and beta-TrCP is less efficient in human breast cancer cells than in non-tumorigenic human mammary epithelial cells. Furthermore, we demonstrate that both PRLr degradation and PRLr phosphorylation on Ser349 are impaired in breast tumor cells and tissues, an observation that directly correlates with enhanced expression of the PRLr in malignant breast epithelium. These findings represent a novel mechanism through which altered PRLr stability may directly influence the pathogenesis of breast cancer.

Stoichiometric structure-function analysis of the prolactin receptor signaling domain by receptor chimeras.

The intracellular domain of the prolactin (PRL) receptor (PRLr) is required for PRL-induced signaling and proliferation. To identify and test the functional stoichiometry of those PRLr motifs required for transduction and growth, chimeras consisting of the extracellular domain of either the alpha or beta subunit of human granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor (GM-CSFr) and the intracellular domain of the rat PRLr were synthesized. Because the high-affinity binding of GM-CSF results from the specific pairing of one alpha- and one beta-GM-CSFr, use of GM-CSFr/PRLr chimera enabled targeted dimerization of the PRLr intracellular domain. To that end, the extracellular domains of the alpha- and beta-GM-CSFr were conjugated to one of the following mutations: (i) PRLr C-terminal truncations, termed alpha278, alpha294, alpha300, alpha322, or beta322; (ii) PRLr tyrosine replacements, termed Y309F, Y382F, or Y309+382F; or, (iii) PRLr wild-type short, intermediate, or long isoforms. These chimeras were cotransfected into the cytokine-responsive Ba/F3 line, and their expression was confirmed by ligand binding and Northern and Western blot analyses. Data from these studies revealed that heterodimeric complexes of the wild type with C-terminal truncation mutants of the PRLr intracellular domain were incapable of ligand-induced signaling or proliferation. Replacement of any single tyrosine residue (Y309F or Y382F) in the dimerized PRLr complex resulted in a moderate reduction of receptor-associated Jak2 activation and proliferation. In contrast, trans replacement of these residues (i.e., alphaY309F and betaY382F) markedly reduced ligand-driven Jak2 activation and proliferation, while cis replacement of both tyrosine residues in a single intracellular domain (i.e., alphaY309+382F) produced an inactive signaling complex. Analysis of these GM-CSFr-PRLr complexes revealed equivalent levels of Jak2 in association with the mutant receptor chains, suggesting that the tyrosine residues at 309 and 382 do not contribute to Jak association, but instead to its activation. Heterodimeric pairings of the intracellular domains from the known PRLr receptor isoforms (short-intermediate, short-long, and intermediate-long) also yielded inactive receptor complexes. These data demonstrate that the tyrosine residues at 309 and 382, as well as additional residues within the C terminus of the dimerized PRLr complex, contribute to PRL-driven signaling and proliferation. Furthermore, these findings indicate a functional requirement for the pairing of Y309 and Y382 in trans within the dimerized receptor complex.

Expression of maturation-specific nuclear antigens in differentiating human myeloid leukemia cells.

The expression of three myeloid-specific nuclear antigens was studied by indirect immunofluorescence with murine monoclonal antibodies in human myeloid (HL-60, ML-2, KG-1, and B-II) leukemia cells treated with chemical inducers of cell differentiation. Treatment of the promyelocytic HL-60 cells with dimethyl sulfoxide or 1,25-dihydroxyvitamin D3 induced the cells to acquire a phenotype that resembled that of granulocytes and monocytes-macrophages, respectively. These phenotypes were characterized by changes in cell growth, cell morphology, expression of specific cell surface antigens, and activities of lysozyme and nonspecific esterase enzymes. Induction of these differentiation markers in the HL-60 cells was associated with induction of the myeloid-specific nuclear antigens. The ML-2 cells, which are arrested at the myeloblast-promyelocyte stage, were also susceptible to the induction of cell differentiation and to changes in the expression of the nuclear antigens, but the degree of susceptibility was less than in the HL-60 cells. The less-differentiated KG-1 and B-II myeloid cells were either not responsive or responded only in a limited degree to the induction of cell differentiation or to changes in the expression of the nuclear antigens. We suggest that the reactivity of cells with monoclonal antibodies to specific nuclear antigens can be used as a maturational marker in cell differentiation studies. Furthermore, nuclear antigens expressed early in cellular differentiation may provide information about changes in regulatory elements in normal and malignant cells.

Simultaneous nuclear antigen and DNA content quantitation using paraffin-embedded colonic tissue and multiparameter flow cytometry.

The simultaneous quantitation of nuclear antigens and DNA content is presented using monoclonal antibodies and flow cytometric analysis, with paraffin-embedded human colonic pathology specimens utilized as source material. The monoclonal antibodies evaluated were shown by immunogold electron microscopy to recognize nuclear proteins preferentially associated with interchromatin (p105) and heterochromatin (p34) regions. Indirect immunofluorescence analysis of p105 revealed two distinct G1-G0 cell subpopulations in cells from normal colonic epithelium and colonic adenocarcinomas. In addition, enhanced levels of both p105 and p34 were observed in aneuploid DNA content stemlines, relative to diploid cells. Cell-sorting experiments performed on cells sorted on the basis of p105 and DNA contents reveal the capability of this method for identifying morphologically heterogeneous cell subpopulations. Other data suggest that p105 is differentially expressed in well-differentiated versus poorly differentiated tumor regions. The potential utility of this approach for the retrospective study of proliferation-associated antigens and protooncogene protein products is discussed.

An old epithelial cell never dies, it just agonesces away.

The behavior of mammary epithelial cells during aging is dynamic and is likely to have significant implications in the pathogenesis of human breast cancer. The growth of epithelial cells over time was thought to parallel that of their underlying stroma, sequentially undergoing a defined period of growth, followed by senescence and, ultimately, cell crisis or rarely immortalization. Recent findings, however, suggest that the evolution of mammary epithelium at the proliferative and chromosomal levels is distinct from that of stroma, contributing to the neoplastic susceptibilities of epithelial cells.

The protein tyrosine kinase P59fyn is associated with prolactin (PRL) receptor and is activated by PRL stimulation of T-lymphocytes.

The clonal expansion of antigen-stimulated T-lymphocytes during an immune response is mediated by several lymphokines. Strong evidence now exists that the neuroendocrine hormone PRL is necessary, but not sufficient, for T-cell proliferation. Little is known, however, of the signal transduction mechanisms of the PRL receptor (PRLR) within T-cells. We demonstrate here that PRL stimulation of the T-cell line Nb2 induced the concentration- and time-dependent activation of the protein tyrosine kinase p59fyn, but not of four other src family protein tyrosine kinases. Activation of fyn was also observed in Concanavalin-A-primed peripheral blood lymphocytes stimulated with PRL and in Nb2 cells incubated with anti-PRLR antibodies. The activation of fyn by PRL stimulation correlated with Nb2 cell proliferation. Immunoblot analysis of anti-fyn and anti-PRLR immune complexes revealed an association between each PRLR isoform and p59fyn. These studies demonstrate for the first time an association between the PRLR and a src family protein tyrosine kinase affiliated with signal transduction.

Activation and association of the Tec tyrosine kinase with the human prolactin receptor: mapping of a Tec/Vav1-receptor binding site.

Stimulation of the PRL receptor (PRLr) results in the activation of the guanine nucleotide exchange factor (GEF) p95Vav1 with corresponding alterations in cytoarchitecture and cell motility. To better understand the mechanisms involved in the regulation of Vav1 activity, the role of the tyrosine kinase p70Tec was examined. Coimmunoprecipitation and in vitro kinase assays revealed that ligand stimulation of the PRLr resulted in the rapid activation of Tec and its concomitant association with the PRLR: When coexpressed in COS-1 cells, both Vav1 and Tec were found to associate with the PRLr in the presence of ligand. In the absence of receptor, a constitutive complex between Vav1 and Tec was noted. Both Vav1 and Tec, however, were capable of independent engagement of a bipartite intracellular domain of the PRLR: Deletion mapping studies confined this interaction to residues 323 to 527 of the intracellular domain of the PRLR: Furthermore, Tec enhanced the GEF activity of Vav1 as evidenced by an increase in GTP-bound Rac1. These data would suggest a pivotal function for the formation of a Tec/Vav1/PRLr complex during PRL-driven signal transduction, given the role of Vav1 in the control of cell proliferation and the regulation of Rho family-mediated cytoskeletal alterations.

Role of cyclophilin B in prolactin signal transduction and nuclear retrotranslocation.

The pleiotropic actions of PRL are necessary for mammary growth and differentiation and in vitro lymphoid proliferation. The proximal action of this ligand is mediated by its cell surface receptor via associated networks. PRL action, however, is also associated with the internalization and translocation of this hormone into the nucleus. To delineate the mechanism of this retrotranslocation, a yeast two-hybrid screen was performed and revealed an interaction between PRL and cyclophilin B (CypB). CypB is a peptidyl prolyl isomerase (PPI) found in the endoplasmic reticulum, extracellular space, and nucleus. The interaction between CypB and PRL was subsequently confirmed in vitro and in vivo through the use of recombinant proteins and coimmunoprecipitation studies. The exogenous addition of CypB potentiated the 3H-thymidine incorporation of PRL-dependent cell lines up to 18-fold. CypB by itself was nonmitogenic and did not potentiate the action of GH or other interleukins. CypB did not alter the affinity of the PRL receptor (PRLr) for its ligand, or increase the phosphorylation of PRLr-associated Jak2 or Stat5a. The potentiation of PRL-action by CypB, however, was accompanied by a dramatic increase in the nuclear retrotranslocation of PRL. A CypB mutant, termed CypB-NT, was generated that lacked the wild-type N-terminal nuclear localization sequence. Although CypB-NT demonstrated levels of PRL binding and PPI activity equivalent to wild-type CypB, it was incapable of mediating the nuclear retrotranslocation of PRL or enhancing PRL-driven proliferation. These studies reveal CypB as an important chaperone facilitating the nuclear retrotransport and action of the lactogenic hormones.

Role of Bag-1 in the survival and proliferation of the cytokine-dependent lymphocyte lines, Ba/F3 and Nb2.

The expression and function of the newly identified Bcl-2- and Raf-1- binding protein, Bag-1, during the cytokine-regulated growth of B and T cell lines was examined. Immunoblot analysis of lysates from the interleukin-3 (IL-3)-dependent B cell line Ba/F3, and the PRL-dependent T cell line Nb2, revealed that variations in Bag-1 levels paralleled alterations in cellular proliferation, viability, and apoptosis induced by the presence or absence of growth factor. To test whether up-regulation of Bag-1 levels altered cellular survival and proliferation, Ba/F3 cells were transfected with a Bag-1 expression construct. The overexpression of Bag-1 in transfected Ba/F3 cells induced an IL-3-independent state. Such transfectants demonstrated sustained viability and proliferation, with minimal apoptosis, in the complete absence of exogenous IL-3. Bag-1 expression was also compared in glucocorticoid-sensitive Nb2 cells and a PRL-independent, glucocorticoid-resistant subline, SFJCD1, during culture of these lines in dexamethasone (Dex). Bag-1 levels were profoundly decreased by the addition of Dex to Nb2 cells, precedent to the onset of apoptotic cell death. In contrast, Dex treatment or PRL withdrawal had no effect on levels of Bag-1 within the SFJCD1 line. These findings establish that the overexpression of Bag-1 in the appropriate cellular context promotes cellular survival and growth, events that may result from the juxtaposition of this protein with mitogenic and antiapoptotic signaling pathways.

Inhibition of ornithine decarboxylase activity and cell proliferation by ultraviolet B radiation in EGF-stimulated cultured human epidermal keratinocytes.

Irradiation of EGF-stimulated human keratinocytes in vitro with ultraviolet B (UVB) radiation inhibited both ornithine decarboxylase (ODC) activity and cellular proliferation. A dose-dependent reduction in ODC activity occurred in primary cultures of adult facial keratinocytes and neonatal foreskin keratinocytes, and in an SV40-transformed keratinocyte cell line derived from neonatal foreskin. When SV40-transformed keratinocytes were treated with epidermal growth factor (EGF), ODC activity was induced up to 21 times in the absence of ultraviolet radiation. However, pre-treatment with UVB significantly reduced the EGF induction of ODC. For example, 85% less ODC activity was observed in cultures treated with EGF (10 ng/ml) plus 2.5 mJ/cm2 of UVB than cultures treated with EGF alone. To assess the effect of UVB on cell proliferation, normal human epidermal keratinocytes grown in medium containing EGF were irradiated with 5 and 10 mJ/cm2 UVB. At days 3 and 5 post-irradiation a significant (up to 78%) decrease in proliferation was observed. Nevertheless, the mean proportion of viable to dead cells remained similar in both UVB-treated and non-irradiated cell cultures. Northern blot analysis of total RNA isolated from irradiated and sham-irradiated cultures showed that UVB caused approximately a one third reduction in steady-state ODC mRNA levels in EGF-stimulated keratinocyte cultures. Because ODC is an enzyme required for cell proliferation, we propose that the UVB-induced decrease in cell proliferation may result at least in part from UVB inhibition of ODC mRNA accumulation and reduced enzyme activity.

Prolactin as a chemoattractant for human breast carcinoma.

Prolactin (PRL) is recognized as a growth and differentiating hormone in the human breast. These effects are mediated by the PRL receptor (PRLr); when stimulated the PRL-PRLr complex activates several signaling cascades, including those involving the GTP-binding proteins Ras and Rac. The activation of these signaling pathways has been associated with cytoskeletal alterations and increased cellular motility. We hypothesized that such changes could occur in PRL-stimulated human breast cancer cells. To test this hypothesis, complementary studies, including wound closure, time-lapse video microscopy (TLVM), and Boyden chamber assay were performed. These studies revealed that PRL significantly enhanced the migration of the breast cancer cell lines T47D, MCF7, and MDA23 1. Co-stimulation with PRL was noted to potentiate epidermal growth factor (EGF)-induced cell motility. IF microscopy of filamentous actin using rhodamine-conjugated phalloidin revealed a significant and rapid generation of both membrane ruffling and stress fibers in response to PRL, an effect inhibited by the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002. In sum, these data reveal that PRL stimulation modulates the cytoskeleton and induces the motility of human breast cancer cells in vitro, events that have been associated with the progression of mammary carcinoma in vivo. Given the recently delineated autocrine-paracrine role for PRL in human breast cancer, these findings could be of appreciable clinical significance.

Interleukin-2 driven nuclear translocation of prolactin in cloned T-lymphocytes.

The nuclear translocation of PRL is demonstrated at the immunofluorescence and electron microscopic (EM) levels in interleukin-2 (IL2)-stimulated cloned T-cells and concanavalin A-stimulated splenocytes. This translocation occurs 2-10 h after IL2 stimulation, and is reversed by the addition of anti-PRL antiserum into the extracellular culture medium. The nuclear localization of PRL in IL2 stimulated T-cells was confirmed by postembedding immunogold EM. The nuclear uptake of PRL after IL2 stimulation was further documented by EM studies using PRL-colloidal gold conjugates. These studies suggest that the intranuclear PRL is translocated from the extracellular medium via an endosomal/lysosomal pathway over a period of several hours. Finally, the requirement for PRL no later than 6 h after IL2 stimulation is demonstrated through the reversible inhibition of T-cell growth with anti-PRL antiserum.

Requirement for prolactin during cell cycle regulated gene expression in cloned T-lymphocytes.

The neuroendocrine hormone PRL acts as a progression factor during interleukin-2 (IL2) stimulated lymphocyte proliferation. Since the sequential expression of cell cycle regulated genes occurs during this process, we examined the contribution of IL2 and PRL to specific RNA accumulation. Stimulation of the cloned T cell line L2 with IL2 and PRL induced the sequential expression of interferon regulatory factor-1, c-myc, proliferating cell nuclear antigen, thymidine kinase, cyclin B, and histone H3. Stimulation of L2 cells with PRL alone, however, induced only the expression of interferon regulatory factor-1. Depletion of PRL, through the use of an anti-PRL antiserum, inhibited IL2 driven proliferation and the expression of cyclin B and histone H3. These results demonstrate that PRL may regulate T cell proliferation by enhancing the expression of some genes necessary for entry into S-phase.

Expression of prolactin and its receptor in human breast carcinoma.

The growth regulatory effects of PRL on the human breast are mediated by its receptor (PRLr), a member of the cytokine receptor family. Recent reverse transcriptase-PCR studies by our laboratory and others have shown PRL expression within breast tissues at the RNA level. To confirm the role of this growth factor-receptor complex in normal and malignant breast tissues, the expression of PRL and PRLr was examined in parallel with the estrogen receptor (ER) and progesterone receptor (PR). Sixty-nine cases of primary invasive breast carcinoma were examined for PRL and PRLr expression by in situ hybridization and immunohistochemical technique, respectively. These data revealed widespread expression of PRL and its receptor in the breast cancers studied (>95%) and in the normal breast tissues (>93%), with no association between the expression of PRL-PRLr and ER or PR. These findings stand in contrast to prior RIA-based studies that detected the PRLr in only 20-60% of breast carcinomas, most commonly in ER-PR-positive cells. These results confirm prior data indicating the presence of an autocrine/paracrine loop for the PRL-PRLr complex within human breast tissues. Given the widespread expression of PRL-PRLr in breast cancer, pharmacological interventions aimed at the inhibition of function of this growth regulatory receptor complex may be of considerable utility in the therapy of this disease.

Use of immunogold electron microscopy and monoclonal antibodies in the identification of nuclear substructures.

A cytochemical technique for the ultrastructural localization of unique nuclear antigens is reported. Using a post-embedding indirect immunogold labeling procedure, nuclear antigens in electron-dense regions of the nucleus are localized with a minimum of nonspecific staining. Using this technique and indirect immunofluorescence, a panel of antinuclear monoclonal antibodies is shown to recognize preferentially cell cycle-dependent nuclear substructures. The antigenic domains recognized include specific regions in condensed chromatin, interchromatin granules, euchromatin, and chromosomes. The specificity of antigen recognition is demonstrated with qualitative and quantitative immunogold electron microscopy and immunoblot analysis. These results reveal the existence of previously undefined supramolecular organization within the nucleus and demonstrate the utility of the immunogold procedure when monoclonal antibodies are used.

Assessment of cell cycle-associated antigen expression using multiparameter flow cytometry and antibody-acridine orange sequential staining.

A novel approach which enables direct assessment of the differential expression of cellular antigens in noncycling (G0) and cycling cell subpopulations is presented. The method involves flow cytometric analysis and sorting of cells stained by use of indirect immunofluorescence, followed by restaining using acid acridine orange, to relate the immunofluorescence of sorted lymphoid subpopulation(s) to cell proliferation status (i.e., G0 vs. G1 vs. S vs. G2 and M). In the present study, this technique successfully identifies the proliferation-associated modulation of a heterochromatin-associated antigen in pokeweed mitogen-stimulated human lymphoid cultures. The potential utility of this method for documenting early antigenic changes associated with the G0-G1 transition is discussed.

Flow cytometric analysis of DNA content in Hürthle cell adenomas and carcinomas of the thyroid.

Paraffin-embedded surgical biopsy material from 17 Hürthle cell tumors of the thyroid was examined for DNA content by flow cytometry to assess the diagnostic and prognostic utility of ploidy determinations in these rare tumors. Both adenomas (11 cases) and carcinomas (6 cases) were studied. As a control for methods, ten randomly selected normal autopsy thyroids were analyzed, all of which demonstrated normal diploid DNA content. Among the Hürthle cell tumors, however, aneuploid peaks were present in six adenomas (55%) and in four carcinomas (67%). Similarly, polyploid DNA peaks in the absence of other aneuploid peaks were present in two adenomas and two carcinomas (18% and 33%, respectively). These findings demonstrate the limited value of aneuploidy or polyploidy as diagnostic features for malignancy in Hürthle cell tumors of the thyroid. As for prognosis, there does not appear to be any unfavorable prognostic significance for abnormal DNA content in histologically benign Hürthle cell tumors treated by surgical excision because no metastases or recurrences occurred in this group at a mean disease-free follow-up of 50 +/- 19 months for six aneuploid lesions and 19 +/- 7 months for two polyploid adenomas. Preliminary data suggest that aneuploidy may, however, have an important prognostic value for histologically defined Hürthle cell carcinomas, because the only patient to die from the tumor in this series had an aneuploid Hürthle carcinoma. Thus, the authors' data indicate that the diagnostic utility of DNA content in Hürthle cell tumors is extremely limited and that there does not appear to be any negative prognostic significance for aneuploidy in histologically defined Hürthle cell adenomas.