PRAME Expression in Endometrioid and Serous Endometrial Carcinoma: A Potential Immunotherapeutic Target and Possible Diagnostic Pitfall.

Preferentially expressed antigen in melanoma (PRAME) is a cancer testes antigen initially employed as a diagnostic marker for melanoma. Although negative in most normal tissues, its expression has been reported in benign endometrial glands. Additionally, PRAME expression has been identified in a growing list of solid and hematologic malignancies and is of interest as a predictive biomarker, as cancer vaccination strategies and adoptive T-cell transfer targeting this molecule are under clinical investigation; additionally, PRAME may identify candidates for retinoid therapy. However, expression of PRAME has not been well-studied in endometrial cancers. We herein evaluate PRAME expression in endometrial carcinomas to better characterize its limitations as a diagnostic melanoma marker as well as its potential as a predictive biomarker in endometrial carcinomas. PRAME expression was evaluated in 256 endometrioid (n=235) and serous (n=21) endometrial carcinomas via tissue microarray. In all, 89% (227/256) demonstrated some degree of nuclear PRAME expression, including 88% (207/235) of endometrioid carcinomas and 95% (20/21) of serous carcinomas. Diffuse (>50%) expression was observed in 70% (179/256) of all cases, including 69% (163/235) of endometrioid carcinomas and 76% (16/21) of serous carcinomas. There was no association between degree of expression and grade, mismatch repair protein status, or stage. The widespread expression of PRAME in endometrial carcinomas suggests this marker should not be interpreted as specific for melanoma in this context. However PRAME may have utility as a predictive biomarker in endometrial cancer, and expansion of testing of PRAME-based therapies to endometrioid and serous endometrial carcinomas may lead to new therapeutic options for these endometrial cancer subtypes.

Dichloroacetate enhances apoptotic cell death via oxidative damage and attenuates lactate production in metformin-treated breast cancer cells.

The unique metabolism of breast cancer cells provides interest in exploiting this phenomenon therapeutically. Metformin, a promising breast cancer therapeutic, targets complex I of the electron transport chain leading to an accumulation of reactive oxygen species (ROS) that eventually lead to cell death. Inhibition of complex I leads to lactate production, a metabolic byproduct already highly produced by reprogrammed cancer cells and associated with a poor prognosis. While metformin remains a promising cancer therapeutic, we sought a complementary agent to increase apoptotic promoting effects of metformin while attenuating lactate production possibly leading to greatly improved efficacy. Dichloroacetate (DCA) is a well-established drug used in the treatment of lactic acidosis which functions through inhibition of pyruvate dehydrogenase kinase (PDK) promoting mitochondrial metabolism. Our purpose was to examine the synergy and mechanisms by which these two drugs kill breast cancer cells. Cell lines were subjected to the indicated treatments and analyzed for cell death and various aspects of metabolism. Cell death and ROS production were analyzed using flow cytometry, Western blot analysis, and cell counting methods. Images of cells were taken with phase contrast microscopy or confocal microscopy. Metabolism of cells was analyzed using the Seahorse XF24 analyzer, lactate assays, and pH analysis. We show that when DCA and metformin are used in combination, synergistic induction of apoptosis of breast cancer cells occurs. Metformin-induced oxidative damage is enhanced by DCA through PDK1 inhibition which also diminishes metformin promoted lactate production. We demonstrate that DCA and metformin combine to synergistically induce caspase-dependent apoptosis involving oxidative damage with simultaneous attenuation of metformin promoted lactate production. Innovative combinations such as metformin and DCA show promise in expanding breast cancer therapies.

Dichloroacetate and Quercetin Prevent Cell Proliferation, Induce Cell Death and Slow Tumor Growth in a Mouse Model of HPV-Positive Head and Neck Cancer.

Elevated glucose uptake and production of lactate are common features of cancer cells. Among many tumor-promoting effects, lactate inhibits immune responses and is positively correlated with radioresistance. Dichloroacetate (DCA) is an inhibitor of pyruvate dehydrogenase kinase that decreases lactate production. Quercetin is a flavonoid compound found in fruits and vegetables that inhibits glucose uptake and lactate export. We investigated the potential role and mechanisms of DCA, quercetin, and their combination, in the treatment of HPV-positive head and neck squamous cell carcinoma, an antigenic cancer subtype in need of efficacious adjuvant therapies. C57Bl/6-derived mouse oropharyngeal epithelial cells, a previously developed mouse model that was retrovirally transduced with HPV type-16 E6/E7 and activated Ras, were used to assess these compounds. Both DCA and quercetin inhibited colony formation and reduced cell viability, which were associated with mTOR inhibition and increased apoptosis through enhanced ROS production. DCA and quercetin reduced tumor growth and enhanced survival in immune-competent mice, correlating with decreased proliferation as well as decreased acidification of the tumor microenvironment and reduction of Foxp (+) Treg lymphocytes. Collectively, these data support the possible clinical application of DCA and quercetin as adjuvant therapies for head and neck cancer patients.

Comparison of Interleukin-1 Ligand Expression by Human Papilloma Virus Status in HNSCCs.

Interleukin-1 alpha (IL-1α) is a cytokine involved in the acute phase immune response and its expression is upregulated in a variety of solid tumors including head and neck squamous cell carcinomas (HNSCCs). Tumor expression of IL-1α is associated with increased tumor aggressiveness in HNSCCs, but this has yet to be studied in the context of human papilloma virus (HPV) status. This study is aimed at determining differences in tumor expression and subcellular localization of IL-1α in HPV-positive (HPV+) and HPV-negative (HPV-) HNSCC tumors. Tissue microarrays (TMAs) containing HPV+ (n = 31) and HPV- (n = 47) primary and metastatic HNSCCs were analyzed for IL-1α expression using immunohistochemical (IHC) staining. HPV status was confirmed using p16 IHC staining and RNA in situ hybridization (RNA ISH). Differences in IL-1α protein expression and secretion in HPV+ and HPV- HNSCC cell lines were determined by western blot and ELISA respectively. Associations between tumor IL1A expression and survival outcomes were assessed in HPV+ and HPV- HNSCC patients from publicly available gene expression datasets. Tumor expression of IL-1α was significantly increased in HPV- tumors and cell lines (as detected by IHC and western blot respectively) compared to HPV+ tumors and cell lines. There was no difference in IL-1α release between HPV+ and HPV- cell lines. IL-1α was expressed in both nuclear and cytoplasmic compartments, with predominant expression in the nucleus. Gene expression of IL1A was significantly increased in HPV-tumors/cell lines compared to HPV+ tumors/cell lines. Lastly, increased IL1A gene expression was significantly associated with worse survival in HPV- tumors but not in HPV+ tumors. Overall IL-1α expression particularly in the nucleus may possess more prognostic significance in HPV- tumors rather than HPV+ tumors. This work warrants further investigation into the role of intracellular IL-1α ligand expression in HNSCCs and may have important implications in IL-1 pathway blockade as therapeutic strategy.

S100 and CD34 Expressing Mesenchymal Neoplasm With Rare PLEKHH2::ALK Fusion and Response to ALK Inhibition.

The PLEKHH2::ALK fusion is a rarely reported gene fusion identified predominantly in lung adenocarcinomas. Tumors with this fusion have been reported to be of durable response to ALK inhibitors. We herein present the case of a 21-year-old woman with a histomorphologically heterogenous mesenchymal neoplasm of the pelvis, expressing both s100 and CD34, with subsequently identified PLEKHH2::ALK fusion. To our knowledge, only a single mesenchymal neoplasm with this gene fusion has been previously reported. We propose that this tumor represents one with a novel ALK fusion in the emerging family of s100 and CD34 expressing mesenchymal neoplasms with oncogenic kinase alterations akin to NTRK -rearranged mesenchymal neoplasms, rather than inflammatory myofibroblastic tumor. Importantly, this tumor demonstrated a significant response to the ALK inhibitor brigatinib.

Galectin-3 Expression in High-Risk HPV-Positive and Negative Head & Neck Squamous Cell Carcinomas and Regional Lymph Node Metastases.

Despite higher stages at presentation, patients with high-risk (HR) HPV-related (HPV+) head and neck squamous cell carcinomas (HNSCCs) have better survival rates compared to those with non-HPV-related (HPV-) disease. However, significant comorbidity and the number of patients who suffer failed treatment, recurrent disease, late metastasis, and death are increasing along with the incidence of HPV+ HNSCC. A cytotoxic T-cell-dependent immune response is required to clear these antigenic cancers. This provides a unique opportunity to employ immune modulators in therapy. Galectin-3 (Gal-3) is a lectin and glycoprotein involved in numerous immunosuppressive functions. Inhibitors are currently under clinical investigation for various diseases. Gal-3 expression was evaluated in HR-HPV+ and HPV- HNSCCs and regional lymph node metastases by tissue microarray. HR-HPV+ cases were more likely to be Gal-3-positive (Gal+) [50% (14/28)] than HPV- cases [18% (9/50), p = 0.004]. No difference in the number of Gal+ cases was identified between primary [30% (16/53)] and metastatic [28% (7/25)] cancers (p = 1); 53% (9/17) of primary HPV+ cancers were Gal+ and 45% (5/11) of metastatic HPV+ cancers were Gal+ (p = 1). Nineteen percent (7/36) of primary HPV- cancers were Gal+ and 14% (2/14) of metastatic HPV- cancers were Gal+ (p = 1). Gal-3 positivity was observed in a subset of HNSCC, suggesting a potential role for therapeutic inhibition in this tumor type. The significantly higher rates of expression seen in HR-HPV+ versus HPV- HNSCC suggest particular promise in the setting of HPV infection. The relatively consistent Gal-3 expression rates observed between metastatic and primary tumors argues against progressive Gal-3 expression in metastasis.

Global Health Education in Pathology Residency.

OBJECTIVES: Pathology and laboratory medicine (PALM) services in low- and middle-income countries are essential to combat the increasing prevalence of cancer in addition to providing documentation of cancer types and trends for future allocation of public health resources. There are many ways PALM as a whole can engage on the global health front. This study summarizes the efforts and results of a global health educational and clinical elective for pathology residents in Quetzaltenango, Guatemala. METHODS: Pathology residents led and implemented the project, working alongside an in-country pathologist and project collaborator to instill project sustainability and allow for future capacity building. RESULTS: An educational elective was established between the pathology departments of the University of Virginia and Hospital Regional de Occidente in Quetzaltenango, Guatemala. Two residents at a time engaged in a month-long educational elective assisting and learning from the in-country pathologist in anatomic pathology clinical work. CONCLUSIONS: The project is an example of a global health initiative centering on the enhancement of PALM services in a low-resource environment via a bidirectional, sustainable educational exchange.

Cytodiagnosis and protein typing of amyloid from a vitreous washing: initial diagnostic workup of hereditary amyloidosis.

Hereditary amyloidosis is a challenging but critical diagnosis, with serious implications with regard to treatment and disease surveillance for both patients and their families. Systemic symptomology is often vague. As vitreous amyloid deposition is strongly linked to the systemic, hereditary disease, its cytodiagnosis in the vitreous may be the incipient finding of hereditary amyloidosis. We describe a 64-year-old man with a history of heart disease and peripheral neuropathy who presented with asymmetric visual disturbances and vitreous opacities, leading to diagnostic vitrectomy. Amyloid was identified on a ThinPrep slide of the vitreous sample via Congo red stain. Creation of a cell block from the residual ThinPrep sample allowed for amyloid protein typing, identifying ATTR (transthyretin)-type amyloid and strongly suggesting hereditary amyloidosis. Subsequent sequencing of the patient's TTR gene identified a pathogenic variant that is associated with autosomal dominant hereditary transthyretin-mediated amyloidosis.

Concordance levels of PD-L1 expression by immunohistochemistry, mRNA in situ hybridization, and outcome in lung carcinomas.

Targeted inhibition of programmed cell death-1 (PD-1) and its ligand (PD-L1) has emerged as first-line therapy for advanced non-small cell lung cancer. Although patients with high PD-L1 expression have improved outcomes with anti-PD-1/PD-L1-directed therapies, use as a predictive biomarker is complicated by robust responses in some patients with low-level expression. Furthermore, reported PD-L1 levels in lung cancers vary widely, and discrepancies exist with different antibodies. PD-L1 expression was thus compared by immunohistochemistry (IHC) versus RNA in situ hybridization (ISH) in 112 lung cancers by tissue microarray: 51 adenocarcinoma, 42 squamous cell carcinoma, 9 adenosquamous carcinoma, 5 carcinoid, 3 undifferentiated large cell carcinoma, 1 large cell neuroendocrine carcinoma, and 1 small cell carcinoma. At least 1% tumor cell staining was considered positive in each modality. A positive concordance of only 60% (67/112) was found between IHC and ISH. Fifty percent (56/112) were positive by IHC and 50% (56/112) by ISH; however, 20% (22/112) were ISH positive but IHC negative. Conversely, 21% (23/112) were IHC positive but ISH negative. There was no significant stratification of PD-L1 positivity by histologic subtype. A trend of more PD-L1-positive stage I cancers identified by ISH versus IHC was observed but was not statistically significant (50% [27/54] by IHC and 64% [35/55] by ISH, P = .18). No significant difference in survival was identified, with an average of 5.3 months in IHC versus 5.2 months in ISH-positive cases. The results demonstrate discordance between PD-L1 RNA levels and protein expression in non-small cell lung cancers, warranting comparison as predictive biomarkers.

HPV RNA in situ hybridization can inform cervical cytology-histology correlation.

BACKGROUND: In situ hybridization for human papillomavirus (HPV) messenger RNA (HPV RNA ISH) recently was introduced as an ancillary tool in the diagnosis of cervical squamous intraepithelial lesions, and can aid in the distinction between low-grade squamous intraepithelial lesions (LSILs) versus reactive/negative biopsies. Prior work has shown that up to one-half of cases originally diagnosed as LSIL are reclassified as negative/reactive by expert consensus review of morphology, and negative HPV RNA ISH results most often correlate with an expert diagnosis of negative/reactive. Given that LSIL overdiagnoses on biopsy may result in the erroneous clinical impression that a cervical lesion has been sampled appropriately, the authors proposed that HPV RNA ISH can inform cytology-histology correlation for challenging LSIL biopsies. METHODS: A total of 92 cervical biopsies originally diagnosed as LSIL were reviewed by 3 gynecologic pathologists and reclassified based on consensus opinion of morphology. ISH was performed for high-risk and low-risk HPV E6/E7 mRNA. Prior/concurrent cytology results were collected. RESULTS: Based on expert consensus morphologic review, 49% of biopsies (45 of 92 biopsies) originally diagnosed as LSIL were reclassified as negative, 6.5% (6 of 92 biopsies) were reclassified as high-grade squamous intraepithelial lesion, and 44.5% (41 of 92 biopsies) were maintained as LSIL. The majority of LSIL biopsies reclassified as negative (80%; 36 of 45 biopsies) were HPV RNA negative, whereas 93% of LSIL biopsies (39 of 41 biopsies) and 100% of high-grade squamous intraepithelial lesion biopsies were HPV RNA positive. CONCLUSIONS: LSIL often is overdiagnosed by morphology on biopsy, potentially leading to the false impression that a lesion identified on cytology has been sampled. Performing RNA ISH on biopsies decreases histologic LSIL overdiagnosis, and potentially can prompt further sampling when there is cytology-histology discordance. Cancer (Cancer Cytopathol) 2018. © 2018 American Cancer Society.

HPV E6/E7 mRNA In Situ Hybridization in the Diagnosis of Cervical Low-grade Squamous Intraepithelial Lesions (LSIL).

Cervical low-grade squamous intraepithelial lesions (LSIL) (aka cervical intraepithelial neoplasia, grade 1 [CIN1]) can present considerable diagnostic challenges and are associated with poor interobserver reproducibility and overdiagnosis. Furthermore, ancillary studies such as p16 immunohistochemistry have shown little utility in resolving the LSIL versus negative/reactive differential. Human papillomavirus (HPV) RNA in situ hybridization (ISH) has shown promise as a diagnostic aid in this setting, but has not been studied in a large case series. We herein investigate high-risk and low-risk HPV RNA ISH in 126 cervical biopsies originally diagnosed as LSIL/CIN1 and compare HPV RNA ISH results to expert-adjudicated morphologic diagnosis to assess whether this assay can help routine cases attain the existing "gold standard" of morphologic consensus diagnosis. We also assess whether this criterion standard can be further improved by integration of HPV RNA ISH results. A consensus diagnosis of intraepithelial lesion (CIN1) was confirmed in 61% of cases, whereas 57% were HPV RNA. HPV-RNA positivity was 84% sensitive and 86% specific for an expert-adjudicated diagnosis of CIN1. Conversely, consensus diagnosis was 90% sensitive and 78% specific for the presence of HPV RNA. Integrating RNA ISH into morphologic review led to further reclassification of 10% of cases, resulting in 95% sensitivity and 98% specificity of HPV RNA ISH for a CIN1 diagnosis and 98% sensitivity and 92% specificity of CIN1 for the presence of HPV RNA. These findings suggest that judicious use of HPV RNA ISH can improve the accuracy of LSIL/CIN1 diagnosis for morphologically ambiguous cases.

Gestational Primary Hyperparathyroidism Due to Ectopic Parathyroid Adenoma: Case Report and Literature Review.

Gestational primary hyperparathyroidism (GPHPT) is a rare condition with fewer than 200 cases reported. We present the case of a 21-year-old woman who presented at 10 weeks' gestation with severe hypercalcemia. Laboratory investigation was consistent with primary hyperparathyroidism. Neck ultrasound did not reveal any parathyroid enlargement. Due to the persistence of severe hypercalcemia, she was treated with 4 weeks of cinacalcet therapy, which was poorly tolerated due to nausea and vomiting. At 14 weeks' gestation, she underwent neck exploration with right lower, left upper, and partial right upper parathyroid gland excision. Intra- and postoperative parathyroid hormone (PTH) and calcium levels remained elevated. After a thorough discussion of risks/benefits, the patient requested further treatment. A parathyroid sestamibi scan (PSS) revealed an ectopic adenoma in the left mediastinum. The adenoma was removed via video-assisted thorascopic parathyroidectomy with intraoperative PTH declining to nearly undetectable levels. She ultimately delivered a physically and developmentally normal infant at 37 weeks' gestation. Appropriate treatment of severe GPHPT may prevent the maternal and fetal complications of hypercalcemia. This case, in which cinacalcet therapy and PSS were used, adds to the body of literature regarding treatment of severe GPHPT.

mTOR, metabolism, and the immune response in HPV-positive head and neck squamous cell cancer.

Extensive preclinical studies have identified mammalian target of rapamycin (mTOR) activation as a frequent molecular signature underlying head and neck squamous cell carcinoma (HNSCC), including the distinct clinical subtype that is human papillomavirus (HPV) related, and have demonstrated the potential therapeutic utility of mTOR inhibitors in the treatment of these cancers. Numerous clinical studies have begun to evaluate this potential, however few have selected for and fewer have focused specifically on HPV-related disease. While HPV-positive (HPV+) HNSCC patients have a generally favorable prognosis, the overall number of patients who suffer failed treatment, recurrent disease, metastasis, and death is increasing due to the rapidly increasing incidence of HPV-related cancers. In this review, we discuss the rationale for proposing the adjuvant use of mTOR inhibition in the treatment of HPV+ HNSCC, highlighting the interplay of virally activated mTOR signaling, cellular metabolism, and the anti-tumor immune response.

Metastatic model of HPV+ oropharyngeal squamous cell carcinoma demonstrates heterogeneity in tumor metastasis.

Human papillomavirus induced (HPV+) cancer incidence is rapidly rising, comprising 60-80% of oropharyngeal squamous cell carcinomas (OPSCCs); while rare, recurrent/metastatic disease accounts for nearly all related deaths. An in vivo pre-clinical model for these invasive cancers is necessary for testing new therapies. We characterize an immune competent recurrent/metastatic HPV+ murine model of OPSSC which consists of four lung metastatic (MLM) cell lines isolated from an animal with HPV+ OPSCC that failed cisplatin/radiation treatment. These individual metastatic clonal cell lines were tested to verify their origin (parental transgene expression and define their physiological properties: proliferation, metastatic potential, heterogeneity and sensitivity/resistance to cisplatin and radiation. All MLMs retain expression of parental HPV16 E6 and E7 and degrade P53 yet are heterogeneous from one another and from the parental cell line as defined by Illumina expression microarray. Consistent with this, reverse phase protein array defines differences in protein expression/activation between MLMs as well as the parental line. While in vitro growth rates of MLMs are slower than the parental line, in vivo growth of MLM clones is greatly enhanced. Moreover, in vivo resistance to standard therapies is dramatically increased in 3 of the 4 MLMs. Lymphatic and/or lung metastasis occurs 100% of the time in one MLM line. This recurrent/metastatic model of HPV+ OPSCC retains the characteristics evident in refractory human disease (heterogeneity, resistance to therapy, metastasis in lymph nodes/lungs) thus serving as an ideal translational system to test novel therapeutics. Moreover, this system may provide insights into the molecular mechanisms of metastasis.

mTOR inhibition as an adjuvant therapy in a metastatic model of HPV+ HNSCC.

Effective treatments for recurrent/metastatic human papillomavirus-positive (HPV+) head and neck squamous cell cancer (HNSCC) are limited. To aid treatment development, we characterized a novel murine model of recurrent/metastatic HPV+ HNSCC. Further analysis of the parental tumor cell line and its four recurrent/metastatic derivatives led to preclinical testing of an effective treatment option for this otherwise fatal disease. Reverse phase protein arrays identified key signaling cascades in the parental and recurrent/metastatic cell lines. While protein expression profiles differed among the recurrent/metastatic cell lines, activated proteins associated with the mTOR signaling cascade were a commonality. Based on these data, mTOR inhibition was evaluated as an adjuvant treatment for recurrent/metastatic disease. mTOR activity and treatment response were assessed in vitro by western blot, Seahorse, proliferation, clonogenic, and migration assays. Standard-of-care cisplatin/radiation therapy (CRT) versus CRT/rapamycin were compared in vivo. Low-dose rapamycin inhibited mTOR signaling, decreasing proliferation (43%) and migration (62%) while it enhanced CRT-induced cytotoxicity (3.3 fold) in clonogenic assays. Furthermore, rapamycin re-sensitized CRT-resistant, metastatic tumors to treatment in vivo, improving long-term cures (0-30% improved to 78-100%, depending on the recurrent/metastatic cell line) and limiting lymph node metastasis (32%) and lung metastatic burden (30 fold). Studies using immune compromised mice suggested rapamycin's effect on metastasis is independent of the adaptive immune response. These data suggest a role of mTOR activation in HPV+ HNSCC recurrent/metastatic disease and that adjuvant mTOR inhibition may enhance treatment of resistant, metastatic cell populations at the primary site and limit distant metastasis.

Improved clearance during treatment of HPV-positive head and neck cancer through mTOR inhibition.

Human papillomavirus (HPV)-related head and neck squamous cell carcinoma (HNSCC) incidence is increasing at a near epidemic rate. We investigated whether the mammalian (or mechanistic) target of rapamycin (mTOR) inhibitor, rapamycin, can be used as a concurrent agent to standard-of-care cisplatin/radiation therapy (CRT) to attenuate tumor lactate production, thus enhancing CRT-induced immune-mediated clearance of this antigenic tumor type. A C57Bl/6-derived mouse oropharyngeal epithelial cell line retrovirally transduced with HPV type 16 E6/E7 and human squamous cell carcinoma cell lines were evaluated for their response to rapamycin in vitro with proliferation assays, Western blots, and lactate assays. Clonogenic assays and a preclinical mouse model were used to assess rapamycin as a concurrent agent to CRT. The potential of rapamycin to enhance immune response through lactate attenuation was assessed using quantitative tumor lactate bioluminescence and assessment of cell-mediated immunity using E6/E7-vaccinated mouse splenocytes. Rapamycin alone inhibited mTOR signaling of all cancer cell lines tested in vitro and in vivo. Furthermore, rapamycin administered alone significantly prolonged survival in vivo but did not result in any long-term cures. Given concurrently, CRT/rapamycin significantly enhanced direct cell killing in clonogenic assays and prolonged survival in immunocompromised mice. However, in immunocompetent mice, concurrent CRT/rapamycin increased long-term cures by 21%. Preliminary findings suggest that improved survival involves increased cell killing and enhanced immune-mediated clearance in part due to decreased lactate production. The results may provide rationale for the clinical evaluation of mTOR inhibitors concurrent with standard-of-care CRT for treatment of HPV-positive HNSCC.

Fluorescence microscopy imaging of giant folding in a catanionic monolayer.

The behavior of the catanionic system of dioctadecyldimethylammonium bromide (DODAB) and sodium dodecyl sulfate (SDS) was investigated at 23 +/- 1 degrees C at the air-water interface using a Langmuir trough. The surface pressure as a function of surface area was measured while monitoring domain structures using epifluorescence microscopy. At high surface densities, the monolayer exhibits collapse through reversible folding at about 47 mN m(-1). This corresponds to the DODAB collapse surface pressure. The number of folds increases with the rate of compression speed and is history-dependent.