Guidelines for pathologic diagnosis of malignant mesothelioma: 2012 update of the consensus statement from the International Mesothelioma Interest Group

CONTEXT

Malignant mesothelioma (MM) is an uncommon tumor that can be difficult to diagnose.

OBJECTIVE

To provide updated practical guidelines for the pathologic diagnosis of MM.

DATA SOURCES

Pathologists involved in the International Mesothelioma Interest Group and others with an interest in the field contributed to this update. Reference material includes peer-reviewed publications and textbooks.

CONCLUSIONS

There was consensus opinion regarding (1) distinction of benign from malignant mesothelial proliferations (both epithelioid and spindle cell lesions), (2) cytologic diagnosis of MM, (3) key histologic features of pleural and peritoneal MM, (4) use of histochemical and immunohistochemical stains in the diagnosis and differential diagnosis of MM, (5) differentiation of epithelioid MM from various carcinomas (lung, breast, ovarian, and colonic adenocarcinomas, and squamous cell and renal cell carcinomas), (6) diagnosis of sarcomatoid mesothelioma, (7) use of molecular markers in the diagnosis of MM, (8) electron microscopy in the diagnosis of MM, and (9) some caveats and pitfalls in the diagnosis of MM. Immunohistochemical panels are integral to the diagnosis of MM, but the exact makeup of panels used is dependent on the differential diagnosis and on the antibodies available in a given laboratory. Immunohistochemical panels should contain both positive and negative markers. It is recommended that immunohistochemical markers have either sensitivity or specificity greater than 80% for the lesions in question. Interpretation of positivity generally should take into account the localization of the stain (eg, nuclear versus cytoplasmic) and the percentage of cells staining (>10% is suggested for cytoplasmic membranous markers). These guidelines are meant to be a practical reference for the pathologist.

The separation of benign and malignant mesothelial proliferations

The separation of benign from malignant mesothelial proliferations has emerged as a major problem in the pathology of the serosal membranes. For both epithelial and spindle cell mesothelial processes, true stromal invasion is the most accurate indicator of malignancy, but stromal invasion is often difficult to assess, especially in small biopsies. In the pleural cavity, deep penetration of a thickened and fibrotic pleura or penetration of mesothelial cells into the fat of the chest wall are good indicators of malignancy; however, superficial entrapment of mesothelial cells and glands by organizing effusions is common in benign reactions and needs to be distinguished from invasion. In the peritoneal cavity, invasion of fat or of organ walls is again the most reliable indicator of malignancy, but entrapment of benign cells in organizing granulation tissue or between fat lobules is frequent and confusing. Proliferations confined to the pleural or peritoneal space, particularly linear arrays of atypical mesothelial cells on the free surface, should not be called malignant in the absence of unequivocal invasion. Cytologic atypia is often not helpful in separating benign from malignant reactions, because benign processes are commonly atypical and mesotheliomas are often deceptively monotonous. Densely packed mesothelial cells within the pleural space are frequent in benign reactions, but densely packed mesothelial cells within the stroma favor a diagnosis of malignancy. Organizing effusions (fibrous pleurisy) typically show zonation with high cellularity and cytologic atypia toward the pleural space and increasing fibrosis with decreasing cellularity and lesser atypia toward the chest wall, whereas sarcomatous (including desmoplastic) mesotheliomas do not demonstrate this type of zonation. Elongated capillaries perpendicular to the pleural surface are seen in organizing effusions but are not a feature of sarcomatous mesotheliomas. The combination of a paucicellular storiform pattern, plus invasion of the stroma (including fat and adjacent tissues), or bland necrosis, overtly sarcomatous foci, or distant metastases, is required for the diagnosis of desmoplastic mesothelioma. Necrosis is usually a sign of malignancy but is occasionally seen in benign mesothelial reactions. Keratin staining is useful in indicating the distribution of mesothelial cells, and particularly in demonstrating penetration of mesothelial cells into the stroma or adjacent structures, but is of no help in separating benign and malignant proliferations because both are keratin-positive. Although both p53 and EMA staining have been proposed as markers of mesothelial malignancy, in our experience they are not helpful for the individual case.

Lobe of origin and histologic type of lung cancer associated with asbestos exposure in the Carotene and Retinol Efficacy Trial (CARET)

Lower lobe origin and histologic diagnosis of adenocarcinoma have been described as useful parameters for attributing lung cancer to prior asbestos exposure. To assess whether these characteristics differed between asbestos-exposed individuals and smokers, we evaluated lobe of origin and histologic type of tumors in 78 asbestos-exposed and 214 nonexposed heavy smokers developing lung cancer during the Carotene and Retinol Efficacy Trial (CARET), a prospective cancer chemoprevention trial. Most tumors in both cohorts, regardless of radiographic fibrosis at baseline, originated in upper lobes, representing 67% in asbestos-exposed and 80% in smokers, respectively (adjusted OR for lower lobe = 1.41; 95% CI = 0.69-2.91). Adenocarcinoma represented 32% of lung tumors in the asbestos cohort, and 30% in the smoking cohort (adjusted OR = 0.78; 95% CI = 0.40-1.55), and was inversely associated with radiographic fibrosis (adjusted OR = 0.19; 95% CI = 0.06-0.62). We conclude that neither anatomic site nor histologic cell type of tumors distinguishes effectively between smoking and asbestos as causal factors in development of lung cancer.

Risk factors for lung cancer and for intervention effects in CARET, the Beta-Carotene and Retinol Efficacy Trial

BACKGROUND

Evidence has accumulated from observational studies that people eating more fruits and vegetables, which are rich in beta-carotene (a violet to yellow plant pigment that acts as an antioxidant and can be converted to vitamin A by enzymes in the intestinal wall and liver) and retinol (an alcohol chemical form of vitamin A), and people having higher serum beta-carotene concentrations had lower rates of lung cancer. The Beta-Carotene and Retinol Efficacy Trial (CARET) tested the combination of 30 mg beta-carotene and 25,000 IU retinyl palmitate (vitamin A) taken daily against placebo in 18314 men and women at high risk of developing lung cancer. The CARET intervention was stopped 21 months early because of clear evidence of no benefit and substantial evidence of possible harm; there were 28% more lung cancers and 17% more deaths in the active intervention group (active = the daily combination of 30 mg beta-carotene and 25,000 IU retinyl palmitate). Promptly after the January 18, 1996, announcement that the CARET active intervention had been stopped, we published preliminary findings from CARET regarding cancer, heart disease, and total mortality.

PURPOSE

We present for the first time results based on the pre-specified analytic method, details about risk factors for lung cancer, and analyses of subgroups and of factors that possibly influence response to the intervention.

METHODS

CARET was a randomized, double-blinded, placebo-controlled chemoprevention trial, initiated with a pilot phase and then expanded 10-fold at six study centers. Cigarette smoking history and status and alcohol intake were assessed through participant self-report. Serum was collected from the participants at base line and periodically after randomization and was analyzed for beta-carotene concentration. An Endpoints Review Committee evaluated endpoint reports, including pathologic review of tissue specimens. The primary analysis is a stratified logrank test for intervention arm differences in lung cancer incidence, with weighting linearly to hypothesized full effect at 24 months after randomization. Relative risks (RRs) were estimated by use of Cox regression models; tests were performed for quantitative and qualitative interactions between the intervention and smoking status or alcohol intake. O'Brien-Fleming boundaries were used for stopping criteria at interim analyses. Statistical significance was set at the .05 alpha value, and all P values were derived from two-sided statistical tests.

RESULTS

According to CARET's pre-specified analysis, there was an RR of 1.36 (95% confidence interval [CI] = 1.07-1.73; P = .01) for weighted lung cancer incidence for the active intervention group compared with the placebo group, and RR = 1.59 (95% CI = 1.13-2.23; P = .01) for weighted lung cancer mortality. All subgroups, except former smokers, had a point estimate of RR of 1.10 or greater for lung cancer. There are suggestions of associations of the excess lung cancer incidence with the highest quartile of alcohol intake (RR = 1.99; 95% CI = 1.28-3.09; test for heterogeneity of RR among quartiles of alcohol intake has P = .01, unadjusted for multiple comparisons) and with large-cell histology (RR = 1.89; 95% CI = 1.09-3.26; test for heterogeneity among histologic categories has P = .35), but not with base-line serum beta-carotene concentrations.

CONCLUSIONS

CARET participants receiving the combination of beta-carotene and vitamin A had no chemopreventive benefit and had excess lung cancer incidence and mortality. The results are highly consistent with those found for beta-carotene in the Alpha-Tocopherol Beta-Carotene Cancer Prevention Study in 29133 male smokers in Finland.

Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease

BACKGROUND

Lung cancer and cardiovascular disease are major causes of death in the United States. It has been proposed that carotenoids and retinoids are agents that may prevent these disorders.

METHODS

We conducted a multicenter, randomized, double-blind, placebo-controlled primary prevention trial -- the Beta Carotene and Retinol Efficacy Trial -- involving a total of 18,314 smokers, former smokers, and workers exposed to asbestos. The effects of a combination of 30 mg of beta carotene per day and 25,000 IU of retinol (vitamin A) in the form of retinyl palmitate per day on the primary end point, the incidence of lung cancer, were compared with those of placebo.

RESULTS

A total of 388 new cases of lung cancer were diagnosed during the 73,135 person-years of follow-up (mean length of follow-up, 4.0 years). The active-treatment group had a relative risk of lung cancer of 1.28 (95 percent confidence interval, 1.04 to 1.57; P=0.02), as compared with the placebo group. There were no statistically significant differences in the risks of other types of cancer. In the active-treatment group, the relative risk of death from any cause was 1.17 (95 percent confidence interval, 1.03 to 1.33); of death from lung cancer, 1.46 (95 percent confidence interval, 1.07 to 2.00); and of death from cardiovascular disease, 1.26 (95 percent confidence interval, 0.99 to 1.61). On the basis of these findings, the randomized trial was stopped 21 months earlier than planned; follow-up will continue for another 5 years.

CONCLUSIONS

After an average of four years of supplementation, the combination of beta carotene and vitamin A had no benefit and may have had an adverse effect on the incidence of lung cancer and on the risk of death from lung cancer, cardiovascular disease, and any cause in smokers and workers exposed to asbestos.

Statistical design and monitoring of the Carotene and Retinol Efficacy Trial (CARET)

CARET is a chemoprevention trial of beta-carotene and vitamin A with lung cancer as the primary outcome. Participants at high risk for lung cancer are drawn from two populations: asbestos-exposed workers and heavy smokers. The intervention is a daily combination of 30 mg beta-carotene and 25,000 IU vitamin A as retinyl palmitate. Nearly 18,000 participants will be followed for a mean 6 years, yielding over 100,000 person-years of follow-up. We project that this sample size will have 80% power to detect a 23% decrease in the incidence of lung cancer cases. The purpose of this paper is to present the values of the key sample size parameters of CARET; our schemes for monitoring CARET for sample size adequacy, incidence of side effects, and efficacy of the study vitamins; an overview of the data collected; and plans for the primary, secondary, and ancillary analyses to be performed at the end of the trial. These approaches to the design, monitoring, and analysis of CARET are applicable for many other prevention trials.

Use of electron microscopy in the diagnosis of uncommon lung tumors

We have demonstrated the value of electron microscopy in the study of ten uncommon lung tumors. Ultrastructural examination contributes toward the accurate classification of unusual lung tumors, and may clarify their histogenesis.

[Changes in the serum lipid fractions of malnourished children with and without clinical infection. Paradoxical hypertriglyceridemia in malnutrition]

We have studied the levels of total triglycerides, total cholesterol and high, low and very low density lipoproteins, in serum from undernourished children and from eutrophic controls matched by age, race and socioeconomical condition with the undernourished group. Malnourished children were classified according to the severity of the nutritional deficiency and according to the presence or absence of associated overt infections. Serum lipids fractions were evaluated by colorimetric procedures and by electrophoretic isolation and elution of the desired lipoprotein followed by colorimetric evaluation of the cholesterol content. Increased levels of total triglycerides and very low density lipoproteins were observed in the undernourished group. The rise in the levels of total triglycerides and very low density lipoproteins was more marked in children with moderate and severe undernutrition as well as in undernourished with associated overt infection. In contrast, as expected, serum levels of total cholesterol, high density and low density lipoproteins were significantly diminished in undernourished children. The depression in the amount of total cholesterol, high density and low density lipoproteins was more marked in the severe forms of undernutrition. Increased levels of total triglycerides and very low density lipoprotein could be determined by a defect in the clearance of these lipid fractions due to depressed activity of lipoprotein lipase.

A quick and inexpensive method for removing polysaccharides from plant genomic DNA

A quick and inexpensive method has been demonstrated to remove polysaccharide contamination from plant DNA. Isolated plant genomic DNA with polysaccharide contaminants was dissolved in TE (10 mM Tris-HCl, pH 7.4, 1 mM EDTA) with NaCl ranging from 0.5-3.0 M, then precipitated with two volumes of ethanol. Most of the polysaccharides were removed effectively in a single high-salt precipitation at 1.0-2.5 M NaCl. At 3.0 M NaCl, the salt precipitated out of solution. Purified DNA was easily digested by either HindIII or EcoRI and was satisfactory as a template for PCR. The results show that high-salt precipitation effectively removed polysaccharides and their inhibitory effects on restriction enzyme and Taq polymerase activity.

Diagnosis of diffuse malignant mesothelioma: experience of a US/Canadian Mesothelioma Panel

The experience of the US/Canadian Mesothelioma Panel with its first 200 cases is reviewed. The light microscopic diagnosis, histochemical findings, immunohistochemical findings, and electron microscopic features of malignant mesotheliomas are reviewed in the context of differential diagnosis. Reasons for referral of case material to the panel and lessons from follow-up of difficult and controversial cases are reported. Recommendations to general pathologists are made regarding evaluation and review of possible mesotheliomas.

The unusual spectrum of neuroendocrine lung neoplasms

Neoplasms of the lungs showing neuroendocrine differentiation are classified histologically into the following groups: (1) carcinoid, (2) atypical carcinoid (well-differentiated neuroendocrine carcinoma and malignant carcinoid, (3) small cell neuroendocrine carcinoma (small cell undifferentiated carcinoma and oat cell carcinoma), and (4) large cell neuroendocrine carcinoma (atypical endocrine tumor of the lung and intermediate neuroendocrine carcinoma). Nine examples of neuroendocrine lung carcinomas are discussed that have unusual histologic features that make it difficult to assign them to one of the above groups, have unusual immunohistochemical features, have unusual ultrastructural features, or exhibit a biologic behavior different from what one would have predicted from their morphologic appearance. The findings in these nine cases suggest that the present classification of neuroendocrine lung neoplasms may be too precise and that these neoplasms, like other nonneuroendocrine pulmonary tumors, exhibit a wider morphologic and biologic spectrum than previously appreciated.

Induction of cylindrical confronting cisternae (AIDS inclusions) in Daudi lymphoblastoid cells by recombinant alpha-interferon

Cylindrical confronting cisternae (CCC), also known as test-tube and ring-shaped forms, are frequently present in the cytoplasm of lymphocytes and occasionally in other cells from patients with acquired immunodeficiency syndrome (AIDS). Recent data indicate that the presence of these cisternae and tubuloreticular structures (TRS) in lymphocytes from patients at risk for AIDS is predictive of the development of this syndrome. CCC are formed by an alteration of the membranes of the rough endoplasmic reticulum, but the mechanism by which they are formed or demonstration of their induction by specific agents has not been previously reported. We cultured Daudi lymphoblastoid cells in medium containing recombinant alpha-interferon and induced the formation of both TRS and CCC. The number of CCC formed in Daudi cells was directly proportional to the concentration of interferon used and the length of culture. CCC were in direct continuity with TRS, which were induced in cells by interferon at an earlier time. The percentage of cell sections containing TRS stayed the same or decreased somewhat after 72 hours of culture, whereas the number of CCC increased. Our results indicate that CCC could be present in various cells from patients with AIDS and other diseases as a result of elevated interferon levels in these conditions.

The use of electron microscopy and immunohistochemistry in the diagnosis and understanding of lung neoplasms

This article has presented information concerning the ultrastructural features and, to a lesser degree, the immunohistochemical characteristics of lung neoplasms. Electron microscopy and immunohistochemistry are useful techniques for diagnosing and understanding common and rare lung tumors. Electron microscopy is particularly helpful in accurately diagnosing undifferentiated lung tumors such as large-cell undifferentiated and small-cell undifferentiated carcinomas. Ultrastructural studies of lung tumors have also aided in overall understanding of the histogenesis of these tumors. Electron microscopy and immunohistochemistry are techniques that can be applied to tiny specimens, including those obtained via fine-needle aspiration biopsy, and to cells obtained from pleural fluid. An intelligent use of electron microscopy and immunohistochemistry aids in the diagnosis and understanding of lung neoplasms.

The widespread distribution of Langerhans cells in pathologic tissues: an ultrastructural and immunohistochemical study

Ultrastructural and/or immunohistochemical analysis of approximately 500 specimens revealed widespread distribution of Langerhans cells in pathologic specimens. More than half of the tissue specimens were from patients with a variety of pulmonary diseases. In all specimens in which Langerhans cells were identified ultrastructurally, they were also identified by an immunoperoxidase technique for the visualization of S-100 protein; the latter technique also revealed the dendritic nature of these cells. Langerhans cells were present in 80 to 93 per cent of 66 pulmonary adenocarcinomas and 17 per cent of squamous cell lung cancers; they were not observed in neuroendocrine lung carcinomas or mesotheliomas. They were also observed in benign inflammatory conditions of the lung of several types and in a variety of other malignant neoplasms and disease processes. The Langerhans cells in these tissues varied from few to many. They were most numerous in bronchioloalveolar cell carcinoma, sometimes appearing almost as frequently as tumor cells, and rare in some benign pulmonary conditions and other tumors. The function of Langerhans cells in these conditions is unknown, but they may have an immunologic function, such as antigen processing and presentation to T lymphocytes.

Long-term survival in small-cell carcinoma of the lung: a population experience

Small-cell lung carcinoma (SCLC) is a rapidly progressive and fatal disease. Historically, surgical resection or radiotherapy of the primary tumor has done little to prolong survival, although the use of combination chemotherapy is more effective. Reported here is the survival experience of 1,538 incident cases of SCLC identified through the Surveillance, Epidemiology and End Results Program in western Washington State from 1974 to 1982. The survival experience of this population series is similar to that reported from specialized referral centers. For 71 of 78 persons surviving at least 24 months, the original diagnostic slides were independently reviewed, 47 cases being confirmed as SCLC. No differences were found in actuarial survival estimates between those confirmed and those not confirmed as SCLC. Multivariate survival analysis was conducted to estimate the effects on survival of stage, therapy, age, sex, primary site, and histologic type. All factors except primary site and histologic type significantly influence initial survival rates. However, the only factor related to post--two-year (ie, long-term) survival, once stage is accounted for, is whether surgery was received as a first course of therapy. Those not receiving surgery were at four times the risk of death as those who did. These results indicate that long-term survival can be achieved in patients with SCLC treated in the community, and that the chance of surviving an additional two years for such patients is approximately 40%.

Drowning and near-drowning involving children: a five-year total population study from the City and County of Honolulu

A study of all serious childhood immersion accidents (both drowned and near-drowned cases) is reported from Hawaii. This is a total population-based survey of 140 consecutive cases (0--15 years) occurring during the five-year period (1973--1977. Age-specific, sex-specific, and osmolality-specific (salt versus fresh water) data are presented both for survivors and fatalities. The overall annual drowning rate of 3.1 per 100,000 children at risk is low, for a water-oriented society. The survival rate following loss of consciousness in the water is 73 per cent. There is no evidence from this study that osmolality affected the probability of survival. The rank order of importance of drowning sites is swimming pools, surf, sheltered salt water bathing, domestic bath tubs, fresh water streams, salt water canals, and garden fish ponds. Specific accident rates, by sex, outcome, and site of immersion are also presented. No secular trend in the rate of drowning was observed in this study. Comparison with the only other available total population survey (Australia) of childhood immersions reveals common epidemiological and demographic patterns in modern urban societies and suggests that safety regulations play a role in reducing swimming accidents and fatalities in children.

Possible hepatotoxicity of Doxidan

A patient with chronic constipation developed liver injury and leukopenia following the ingestion of Doxidan, a combination drug consisting of danthron and dioctyl calcium sulfosuccinate. Evidence is presented that dioctyl calcium sulfosuccinate may have potentiated the toxicity. The liver injury was associated with deposition of IgE in the Kupffer cells. The mechanism of toxicity remains unclear.

Lymphomatoid granulomatosis in a renal transplant recipient

Lymphomatoid granulomatosis, as defined by Liebow et al. in 1972, is an angiocentric, angiodestructive, lymphoreticular proliferative disorder of uncertain relationship, if any, to malignant lymphoma. This report describes the rapid development and progression of lymphomatoid granulomatosis in a 33 year old recipient of an immunosuppressed renal transplant. The report further discusses the differences between lymphomatoid granulomatosis and malignant lymphoma with respect to both histology and natural histor.

Prevalence of Mycoplasma hominis and Ureaplasma urealyticum (T strains) in urine of adolescents

Adolescent children were surveyed for colonization with Mycoplasma hominis and Ureaplasma urealyticum by culturing urine specimens. Rates were compared between three study groups: (i) 397 children attending parochial schools, (ii) 293 children attending an adolescent clinic specializing in adjustment problems, and (iii) 86 children attending a renal clinic. The recovery rate was higher among postpubertal girls attending the renal clinic (33%) and the adolescent clinic (26%) than among students attending parochial high school (males 2%, females 8%). Girls had approximately eightfold higher rates than boys of the same age. Isolation of Mycoplasmataceae was associated with certain sociological determinants, such as dating, cigarette smoking, and coming from a broken home, but also with abnormal findings (protein, leucocytes) in urine.

Multiple hormone producing islet cell carcinomas of the pancreas. A morphological and biochemical investigation

Biochemical, light, and electron microscopic studies of two multiple hormone producing metastic islet cell carcinomas of the pancreas are presented. Both tumors initially produced symptoms referable to a single hormone and over a period of years produced two other endocrine active polypeptides. The tumor in case 1 had been studied electron microscopically six years previously and had demonstrated no significant ultrastructural changes since then. The tumor in case 2 contained secretory granules of markedly varying size and density, suggesting a formation of packaged precursor molecules of possibly all three hormones. The pathogenesis of these tumors is discussed in light of recent evidence concerning the origin of endocrine cells.