A comparison of clinically utilized human papillomavirus detection methods in head and neck cancer.

Detection of human papillomavirus (HPV) in head and neck cancer has therapeutic implications. In situ hybridization and immunohistochemistry for p16 are used by surgical pathologists. We compared the sensitivity and specificity of three popular commercial tests for HPV detection in head and neck squamous cell carcinomas with a 'gold standard' HPV PCR assay. A total of 110 prospectively collected, formalin-fixed tumor specimens were compiled onto tissue microarrays and tested for HPV DNA by in situ hybridization with two probe sets, a biotinylated probe for high-risk (HR) HPV types 16/18 (Dako, CA, USA) and a probe cocktail for 16/18, plus 10 additional HR types (Ventana, AZ, USA). The p16(INK4) expression was also assessed using a Pharmingen immunohistochemistry antibody (BD Biosciences, CA, USA). Tissue microarrays were stained and scored at expert laboratories. HPV DNA was detected by MY09/11-PCR, using Gold AmpliTaq and dot-blot hybridization on matched-fresh frozen specimens in a research laboratory. HPV 16 E6 and E7-RNA expression was also measured using RT-PCR. Test performance was assessed by a receiver operating characteristic analysis. HR-HPV DNA types 16, 18 and 35 were detected by MY-PCR in 28% of tumors, with the majority (97%) testing positive for type 16. Compared with MY-PCR, the sensitivity and specificity for HR-HPV DNA detection with Dako in situ hybridization was 21% (95% confidence interval (CI): 7-42) and 100% (95% CI: 93-100), respectively. Corresponding test results by Ventana in situ hybridization were 59% (95% CI: 39-78) and 58% (95% CI: 45-71), respectively. The p16 immunohistochemistry performed better overall than Dako (P=0.042) and Ventana (P=0.055), with a sensitivity of 52% (95% CI: 32-71) and specificity of 93% (95% CI: 84-98). Compared with a gold standard HPV-PCR assay, HPV detection by in situ hybridization was less accurate for head and neck squamous cell carcinoma on tissue microarrays than p16 immunohistochemistry. Further testing is warranted before these assays should be recommended for clinical HPV detection.

Co-expression of GPR30 and ERbeta and their association with disease progression in uterine carcinosarcoma.

OBJECTIVE: We sought to evaluate the expression of G protein-coupled receptor 30 (GPR30) and estrogen receptor (ER)beta in uterine carcinosarcoma (CS). STUDY DESIGN: Immunohistochemistry was performed using antibodies to GPR30, ERbeta, ERalpha, and progesterone receptor (PR). The staining intensity and percentage of positive cells were scored for each tissue section. Expression levels were compared using the Wilcoxon rank sum test. Correlation was evaluated by Spearman rho and logistic regression. RESULTS: Compared with normal endometrium, CS had lower ERalpha and PR expression (both P < .01) but higher GPR30 epithelial expression (P = .03). Advanced-stage CS had higher GPR30 (P < .01) and ERbeta (P = .02) epithelial expression compared with early-stage CS. Expression of GPR30 and ERbeta correlated with each other (P < .01), and not with ERalpha or PR. CONCLUSION: In uterine CS, GPR30 and ERbeta are coordinately overexpressed and expression levels increase in advanced-stage disease, supporting the involvement of alternative ERs in disease progression.

Loss of retinal cadherin facilitates mammary tumor progression and metastasis.

The mammary epithelium is thought to be stabilized by cell-cell adhesion mediated mainly by E-cadherin (E-cad). Here, we show that another cadherin, retinal cadherin (R-cad), is critical for maintenance of the epithelial phenotype. R-cad is expressed in nontransformed mammary epithelium but absent from tumorigenic cell lines. In vivo, R-cad was prominently expressed in the epithelium of both ducts and lobules. In human breast cancer, R-cad was down-regulated with tumor progression, with high expression in ductal carcinoma in situ and reduced expression in invasive duct carcinomas. By comparison, E-cad expression persisted in invasive breast tumors and cell lines where R-cad was lost. Consistent with these findings, R-cad knockdown in normal mammary epithelium stimulated invasiveness and disrupted formation of acini despite continued E-cad expression. Conversely, R-cad overexpression in aggressive cell lines induced glandular morphogenesis and inhibited invasiveness, tumor formation, and lung colonization. R-cad also suppressed the matrix metalloproteinase 1 (MMP1), MMP2, and cyclooxygenase 2 gene expression associated with pulmonary metastasis. The data suggest that R-cad is an adhesion molecule of the mammary epithelium, which acts as a critical regulator of the normal phenotype. As a result, R-cad loss contributes to epithelial suppression and metastatic progression.

Tissue microarray analysis of hormonal signaling pathways in uterine carcinosarcoma.

OBJECTIVES: To evaluate the relationship of hormone (estrogen receptor alpha, estrogen receptor beta, progesterone receptor) and growth factor receptor (insulin-like growth factor receptor, human epidermal growth factor receptor 2) expression with disease progression in uterine carcinosarcoma. STUDY DESIGN: Immunohistochemistry was performed on tissue arrays using standard methodology. Differences between groups were evaluated by the Wilcoxon rank-sum test. Interactions between tumor stage and receptor expression were determined by linear trend analysis. RESULTS: Compared with normal endometrium, carcinosarcomas exhibited low estrogen receptor alpha and progesterone receptor expression (all P < .01), but overexpressed estrogen receptor beta (P = .02). Estrogen receptor beta expression increased in advanced stage disease (P = .02). Insulin-like growth factor receptor expression was lower in carcinosarcoma compared with normal endometrium (P = .01). Human epidermal growth factor receptor 2 expression was elevated and increased with disease progression (P < .01). CONCLUSION: In uterine carcinosarcoma, estrogen receptor beta expression is elevated and increases with disease progression, whereas estrogen receptor alpha and progesterone receptor are suppressed. Human epidermal growth factor receptor 2 expression is increased, whereas insulin-like growth factor receptor is lower than in normal endometrium. These data support a potential role for estrogen receptor beta in disease progression via crosstalk with human epidermal growth factor receptor 2.

Laparoscopic nephrectomy for the management of renal medullary carcinoma in a child.

Renal medullary carcinoma is a lethal subtype of renal cancer that afflicts patients with sickle-cell hemoglobinopathies. Here we present the case of a 13-year-old boy with renal medullary carcinoma who is the first, to our knowledge, to be managed using a planned laparoscopic radical nephrectomy.

Expression of selenium-binding protein 1 characterizes intestinal cell maturation and predicts survival for patients with colorectal cancer.

To identify candidate genes involved in the development of colorectal cancer, we used cDNA microarrays to analyze gene expression differences between human colorectal tumors and paired adjacent normal mucosa. We identified approximately 3.5-fold significant downregulation of selenium-binding protein 1 (SBP1) in colorectal tumors compared to normal mucosa (p = 0.003). Importantly, stage III colorectal cancer patients with low tumor-SBP1 expression had significantly shorter disease-free and overall survival as compared with those patients with high tumor-SBP1 expression (p = 0.04 and 0.03, respectively). We further characterized the role of SBP1 in colorectal cancer in vivo and in vitro. In normal tissue, SBP1 was maximally expressed in terminally differentiated epithelial cells on the luminal surface of crypts in the large intestine. Consistent with this in vivo localization, SBP1 was upregulated during in vitro colonic cell differentiation along the absorptive (Caco-2) and secretory (HT29 Clones 16E and 19A) cell lineages. Downregulation (approximately 50%) of SBP1 expression by small interfering RNA in colonic cancer cells was associated with reduced expression of another epithelial differentiation marker, carcinoembryonic antigen (CEA), although PCNA and p21(WAF1/cip1 )expression were not altered. These data demonstrate that higher expression of SBP1 is associated with differentiation of the normal colonic epithelia and may be a positive prognostic factor for survival in stage III colorectal carcinoma.

Renal medullary carcinoma: the Bronx experience.

OBJECTIVES: Renal medullary carcinoma (RMC) is a devastating and extremely rare malignancy primarily afflicting young men with sickle cell trait. We present our clinical experience with 9 cases of RMC during a 10-year period and briefly review the published data. METHODS: A retrospective chart review of 9 cases of RMC during a 10-year period at our institutions was performed. The clinical patient characteristics, presentations, treatments, and outcomes were recorded. The radiographic images and pathologic specimens were reviewed. Applicable studies were selected from a Medline search. RESULTS: All 9 patients had sickle cell trait, the male/female ratio was 6:3, and the age range was 13 to 31 years. All the patients presented with flank pain, two thirds had hematuria, and 3 of the 9 patients presented with a palpable mass. Eight of the nine tumors were right sided, ranging from 4 to 12 cm in the greatest diameter. Of the 9 patients, 7 underwent radical nephrectomy. One patient was deemed to have unresectable disease by the operating surgeon, and one was given initial chemotherapy after biopsy of a metastatic lesion. The neoadjuvant therapies varied. Overall survival ranged from 4 to 16 months, with 2 patients still living at the last follow-up visit. CONCLUSIONS: Our urban setting likely explains our relatively large experience with this rare and extremely aggressive tumor. An early diagnosis is critical, and a high index of suspicion should be given to any individual with sickle cell trait and new-onset hematuria, especially in the setting of a right-sided mass. Prospective trials are needed for chemotherapy/immunotherapy, because surgical intervention alone is inadequate.

Biventricular mural vegetations in a patient without valvular pathology.

We present the case of a 40 year-old man with biventricular nonvalvular vegetations presenting with acute onset of unilateral hearing loss and headache as a result of septic emboli. The medical literature involving the rare diagnosis of mural vegetation is reviewed and unusual features of this case are discussed.

Caveolin-1 mutations in human breast cancer: functional association with estrogen receptor alpha-positive status.

A Japanese study reported that up to 16% of breast cancer samples harbor a sporadic mutation within the human Cav-1 gene, namely P132L. To date, however, no studies have examined the United States' population. Here, we developed a novel allele-specific real-time PCR assay to detect the Cav-1 P132L mutation in mammary tumor cells isolated by laser capture microdissection from formalin-fixed paraffin-embedded breast cancer samples. We report that the Cav-1 P132L mutation is present in approximately 19% of estrogen receptor alpha (ERalpha)-positive breast cancers but not in ERalpha-negative breast cancers. This is the first demonstration that the P132L mutation is exclusively associated with ERalpha-positive mammary tumors. We also identified six novel Cav-1 mutations associated with ERalpha-positive breast cancers (W128Stop, Y118H, S136R, I141T, Y148H, and Y148S). Thus, the overall incidence of Cav-1 mutations in ERalpha-positive breast cancers approaches 35% (greater than one-third). To mechanistically dissect the functional relationship between Cav-1 gene inactivation and ERalpha expression, we isolated primary mammary epithelial cells from wild-type and Cav-1-/- mice and cultured them in a three-dimensional system, allowing them to form mammary acinar-like structures. Under conditions of growth factor deprivation, Cav-1-deficient mammary acini displayed increased ERalpha levels and enhanced sensitivity toward estrogen-stimulated growth, with specific up-regulation of cyclin D1. Finally, we discuss the possibility that sporadic Cav-1 mutations may act as an initiating event in human breast cancer pathogenesis.

Caveolin-1 immunohistochemical analysis in differentiating chromophobe renal cell carcinoma from renal oncocytoma.

Chromophobe renal cell carcinoma (ChRCC) and oncocytoma might mimic each other histologically. We studied the immunohistochemical staining pattern of caveolin-1 in 21 ChRCCs and 26 oncocytomas and compared it with cytokeratin (CK) 7 to evaluate its usefulness in differentiating these 2 neoplasms. All 21 ChRCCs (100%) were positive for caveolin-1, 20 of which were stained in 20% or more of the tumor cells. In contrast, only 3 (12%) of 26 oncocytomas showed positivity in fewer than 20% tumor cells and 23 (88%) of 26 were negative. In the nonneoplastic kidney, positive caveolin-1 staining was detected in the interstitial blood vessels and the parietal cells of the Bowman capsules but not in the tubular epithelium and glomerular and peritubular capillaries. All 21 ChRCCs (100%) were positive for CK7, with 18 (86%) stained in 20% or more of the tumor cells and 3 (14%) in fewer than 20%. Of 26 oncocytomas, 25 (96%) were positive for CK7, with 7 (27%) stained in 20% or more of the tumor cells and 18 (69%) in fewer than 20%. These results strongly suggest that caveolin-1 immunohistochemical analysis is useful for differentiating ChRCC from oncocytoma and is superior to CK7.

Imaging characteristics of minimal fat renal angiomyolipoma with histologic correlations.

OBJECTIVES: To review our experience with minimal fat angiomyolipomas (AMLs) and correlate the confirmed pathologic diagnosis with preoperative radiologic features to evaluate the feasibility of an accurate diagnosis preoperatively. On rare occasions, renal AMLs contain minimal amounts of fat that are not identified on cross-sectional imaging. METHODS: From November 1998 to August 2003, 6 patients (seven lesions) underwent renal surgery with the preoperative diagnosis of renal cell carcinoma as determined by preoperative imaging studies, and the finding of AML was unexpected. A single pathologist and radiologist reviewed all pathologic specimens and radiologic examinations. The characteristic findings were recorded and compared with those in published reports. RESULTS: Pathologic review of the specimens demonstrated microscopic amounts of mature adipocytes, abnormally thickened blood vessels, and smooth muscle cells in all seven lesions. The mean estimated fat content was 4.1% (range 3% to 10%). Hounsfield unit measurement of the lesions on unenhanced computed tomography images revealed all lesions to be hyperdense relative to the normal kidney parenchyma and enhanced by at least 90 Hounsfield units or more with the administration of intravenous contrast. Enhancement was homogenous throughout each of the seven masses. CONCLUSIONS: Minimal fat renal AML tumors are typically hyperdense relative to the normal kidney parenchyma and demonstrate homogenous enhancement with the administration of intravenous contrast on computed tomography. These results may have important implications when planning partial versus radical nephrectomy by open or minimally invasive techniques.

N-cadherin expression in breast cancer: correlation with an aggressive histologic variant--invasive micropapillary carcinoma.

Upregulation of N-cadherin in epithelial tumor cells has been shown to contribute to the invasive/metastatic phenotype. It remains however to be determined whether N-cadherin is increased in human breast cancers with enhanced malignant potential. We examined a large number of invasive breast cancer specimens (n = 114) for N- and E-cadherin. These specimens compared invasive duct carcinomas (IDCs) of varying histologic grades with an aggressive subtype, invasive micropapillary carcinoma of the breast (MPAP), which has a high propensity for lymphatic invasion and lymph node metastasis. Staining scores for N- and E-cadherin were compared between non-MPAP and MPAP IDCs, and between the invasive and ductal carcinoma in situ (DCIS) of each IDC using statistical analysis. We found that N-cadherin was expressed in 76% of MPAP and 52% of non-MPAP carcinomas, and E-cadherin in 57% of MPAP and 36% of non-MPAP tumors. More MPAP (25%) compared to non-MPAP (5%) tumors expressed both cadherins. Of the two cadherins, N-cadherin was significantly associated with MPAP tumors (p = 0.033) compared to E-cad (p = 0.171). Moreover, in the majority of tumors that were positive for N-cadherin, the staining scores were increased in the IDC relative to intraductal components, and this effect was more dramatic in the MPAP carcinomas. This difference for N-cadherin was greater than the corresponding difference for E-cadherin in the MPAP group (p = 0.005), whereas such changes were not significant in the non-MPAP group (p = 0.10). Thus, N-cadherin is associated with tumor aggressiveness and metastatic potential and may contribute to tumor progression.

Pulmonary crystal-storing histiocytoma.

We describe the case of a 50-year-old woman with a lung tumor composed of crystal-storing histiocytes. These cells and associated plasma cells failed to show clonal light chain restriction, and the patient had no associated hematologic disorder. The differential diagnosis included crystal-storing histiocytosis, characterized by accumulation of crystallized immunoglobulins, a rare manifestation of monoclonal gammopathies/plasma cell dyscrasias. Crystal-laden histiocytes have previously been described in many organs. Four reports have described crystal-storing histiocytosis in the lung, always associated with a lymphoproliferative disorder. The present patient, 1 other case from our archive, and 1 case reported in the literature, all without an association with lymphoproliferative disorder, make a full description and definition of this lesion appropriate. The morphology, immunohistochemical profile, and electron microscopic features are described herein, and the term pulmonary crystal-storing histiocytoma is proposed. A practical algorithm is presented for the assessment of solitary lung masses composed of large histiocytic cells.

Caveolin-3 is a sensitive and specific marker for rhabdomyosarcoma.

Caveolin-3 (Cav-3) is a principal structural protein of caveolae membrane domains. Animal studies have revealed that Cav-3 is expressed in skeletal and cardiac myocytes but absent in other types of cells. Recent studies have shown that abnormalities in the Cav-3 gene are associated with some forms of muscular dystrophy, while skeletal muscle abnormalities have been observed in Cav-3 transgenic and knockout mice. In this study the authors evaluated the distribution of Cav-3 in normal human tissues and compared the expression of Cav-3 with that of myogenin and myoD1 in rhabdomyosarcoma (RMS), malignant mixed mullerian tumor (MMMT), and an array of neoplasms that mimic RMS to assess the utility of Cav-3 as a diagnostic marker for tumors with skeletal muscle differentiation. In nonneoplastic human tissues, crisp membrane staining for Cav-3 was present in cardiac and skeletal myocytes and occasionally in arterial smooth muscle cells and prostatic stromal cells, while other cell types were negative for Cav-3. Eighty-eight percent (21/24) of RMS studied were positive for Cav-3. Positive staining was generally observed in the more maturely differentiated tumor cells but not the primitive tumor cells. Eight of nine cases of MMMT stained strongly with Cav-3 in their rhabdomyosarcomatous component but not in other components. Fifty-four other neoplasms (13 leiomyosarcomas, 8 neuroblastomas, 5 lymphomas, 6 Wilms tumors without skeletal muscle differentiation, 5 Ewing sarcomas, 4 malignant fibrous histiocytomas, 4 angiosarcomas, 6 malignant melanomas, and 3 synovial sarcomas) were negative for Cav-3 expression. Nearly all (96% [23/24]) cases of RMS were positive for myogenin, while 88% (21/24) were positive for myoD1. Primitive tumor cells showed significantly increased expression of myoD1 and myogenin; conversely, more differentiated tumor cells were negative or weakly stained. The rhabdomyosarcomatous component of MMMT stained focally with myogenin and myoD1, in contrast to the strong Cav-3 labeling in these cells. These results demonstrate that Cav-3 is specifically expressed in human cardiac and skeletal myocytes. Furthermore, its high specificity and relatively high sensitivity (88%) for tumors with skeletal muscle differentiation suggest that Cav-3 is a valuable marker for these tumors and may be used to assess the degree of differentiation of RMS and to identify residual tumor cells in post-chemotherapy specimens.

Magmas expression in neoplastic human prostate.

Magmas, is a 13-kDa mitochondrial protein which is ubiquitously expressed in eukaryotic cells. It was identified as a granulocyte-macrophage-colony stimulating factor (GM-CSF) inducible gene in hematopoietic cells and has a key role in the transport of mitochondrial proteins in yeast. Because GM-CSF receptor levels are elevated in prostate cancer, Magmas expression was examined in normal and neoplastic tissue. Magmas protein levels were barely detectable in non-neoplastic prostate glands. Increased amounts were observed in some samples of intraepithelial neoplasia. Approximately one half of the adenocarcinoma samples examined had weak Magmas expression, while the remainder had intermediate to high levels. The increased Magmas observed in malignant tissue was a result of higher protein expression and not from changes in mitochondrial content. Interestingly, in some patients, the normal prostate tissue had more Magmas message than the malignant portion. The results indicated that Magmas expression in prostate cancer is heterogeneous and independent of clinical stage and Gleason score. Further studies are needed to determine if Magmas expression has prognostic significance in prostate cancer.

Immunohistochemical staining for calretinin is useful for differentiating schwannomas from neurofibromas.

We studied 25 cases of schwannoma and 42 cases of neurofibroma immunohistochemically with antibodies to calretinin and S-100 protein to explore the potential usefulness of calretinin in differentiating schwannomas from neurofibromas. Of 25 schwannomas, 24 (96%) showed moderate to strong staining for calretinin, with the extent of staining ranging from focal to diffuse. In contrast, only 3 (7%) of 42 neurofibromas displayed focal weak to moderate staining with calretinin. All 42 cases of neurofibromas and all 25 cases of schwannomas showed diffuse moderate to strong staining with S-100 protein. Calretinin also labeled mast cells, whose presence was confirmed further by staining for c-kit, which commonly was present in both tumor types in a scattered individual cell pattern easily differentiated from the clustered pattern of neoplastic spindle cells. Taken together, these results indicate that calretinin is detected in almost all schwannomas and in only a small percentage of neurofibromas, suggesting it is a useful marker for differentiating schwannomas from neurofibromas. Although mast cells present in these 2 neoplasms also react with calretinin, the pattern of staining can be distinguished easily from that of neoplastic cells.

Repeated testicular infarction in a patient with sickle cell disease: a possible mechanism for testicular failure.

We report a case of repeated testicular infarction in a 39-year-old man with sickle cell disease. The patient presented with a 2-week history of testicular pain and was found clinically and sonographically to have a testicular mass, suspicious for a testicular tumor. The pathologic examination of the orchiectomy specimen revealed multiple infarcts, showing temporal variation ranging from acute (several days old) to recent (2 to 3 weeks old) to remote. This is the fifth case of segmental testicular infarction reported in patients with sickle cell disease/trait. We propose repeated testicular infarction as a probable mechanism of testicular failure and impaired fertility in patients with sickle cell disease.

Expression of caveolin-1 and caveolin-2 in urothelial carcinoma of the urinary bladder correlates with tumor grade and squamous differentiation.

We immunohistochemically evaluated 94 cases of urothelial carcinoma (UC) of the urinary bladder for the expression of caveolin (Cav)-1 and Cav-2. Neither benign urothelium present in 22 cases nor flat carcinoma in situ present in 10 cases stained for Cav-1 or Cav-2. Thirty-five (37%) of 94 cases and 45 (51%) of 89 cases of UC stained positively for Cav-1 and Cav-2, respectively. The percentages of positive cases for Cav-1 in grades 1, 2, and 3 tumors were 0% (0/6), 0% (0/25), and 56% (35/63), respectively (P < .001), and for Cav-2, 0% (0/6), 13% (3/23), and 70% (42/60), respectively (P < .001). Multivariate analysis showed no significant correlation between tumor stage and Cav-1 or Cav-2 expression after correction for tumor grade. Eighty-two percent (14/17) of cases with squamous differentiation were positive for Cav-1 compared with 43% (20/46) of grade 3 tumors without squamous differentiation (P < .001). These results indicate a positive correlation of the expression of Cav-1 and Cav-2 with tumor grade and squamous features of UC and suggest that Cav-1 and Cav-2 be studied further for a possible role in tumor progression and squamous differentiation.

Expression of calretinin and the alpha-subunit of inhibin in granular cell tumors.

Granular cell tumors (GCTs) typically express S-100 protein, which has been used as a marker in differential diagnosis. Calretinin, a calcium-binding protein related structurally to S-100, and inhibin, a polypeptide hormone secreted primarily by ovarian granulosa cells and testicular Sertoli cells and functioning as an inhibitor for pituitary follicle-stimulating hormone secretion, are potentially useful but not well-evaluated markers for GCTs. We studied 43 cases of GCT with antibodies to calretinin, the inhibin alpha-subunit, and S-100 protein. All tumors were positive for inhibin alpha-subunit and S-100 protein, with 50% or more cells showing moderate to strong staining. Forty tumors (93%) were positive for calretinin, ranging from focal weak to diffuse strong staining. Enhanced staining for calretinin in the tumor cells adjacent to hyperplastic squamous epithelium was observed in 9 of 13 cases showing pseudoepitheliomatous hyperplasia. Calretinin and the inhibin alpha-subunit are useful markers for GCTs. The expression of calretinin, a primarily neuronal protein, in GCTs further supports its neural differentiation or derivation. The elevated calretinin expression in the tumor cells adjacent to the hyperplastic squamous epithelium suggests a role for calretinin in the tumor cells-squamous epithelium interaction.

Caveolin-1-deficient mice are lean, resistant to diet-induced obesity, and show hypertriglyceridemia with adipocyte abnormalities.

Caveolae organelles and caveolin-1 protein expression are most abundant in adipocytes and endothelial cells. Our initial report on mice lacking caveolin-1 (Cav-1) demonstrated a loss of caveolae and perturbations in endothelial cell function. More recently, however, observation of the Cav-1-deficient cohorts into old age revealed significantly lower body weights, as compared with wild-type controls. These results suggest that Cav-1 null mice may have problems with lipid metabolism and/or adipocyte functioning. To test this hypothesis directly, we placed a cohort of wild-type and Cav-1 null mice on a high fat diet. Interestingly, despite being hyperphagic, Cav-1 null mice show overt resistance to diet-induced obesity. As predicted, adipocytes from Cav-1 null null mice lack caveolae membranes. Early on, a lack of caveolin-1 selectively affects only the female mammary gland fat pad and results in a near complete ablation of the hypo-dermal fat layer. There are also indications of generalized adipose tissue pathology. With increasing age, a systemic decompensation in lipid accumulation occurs resulting in dramatically smaller fat pads, histologically reduced adipocyte cell diameter, and a poorly differentiated/hypercellular white adipose parenchyma. To gain mechanistic insights into this phenotype, we show that, although serum insulin, glucose, and cholesterol levels are entirely normal, Cav-1 null mice have severely elevated triglyceride and free fatty acid levels, especially in the post-prandial state. However, this build-up of triglyceride-rich chylomicrons/very low density lipoproteins is not due to perturbed lipoprotein lipase activity, a major culprit of isolated hypertriglyceridemia. The lean body phenotype and metabolic defects observed in Cav-1 null mice are consistent with the previously proposed functions of caveolin-1 and caveolae in adipocytes. Our results show for the first time a clear role for caveolins in systemic lipid homeostasis in vivo and place caveolin-1/caveolae as major factors in hyperlipidemias and obesity.