Document 6ad4QkNpoNmRyOJypXn3V5Zm

American Journal of Industrial Medicine 25:611-612 (1994) LETTER TO THE EDITOR Fiber Potency Vs. Importance A Key words: mesothelioma, chrysodle, tremolite, amphlboles, asbestos INTRODUCTION Drs. Hughes and Weill [1994] make the important point that fiber potency with regard to the induction of mesothelioma is-distinct from fiber importance. We totally agree with them regarding this point. As noted in our paper [Roggli et al., 1993], the conventional wisdom regarding mesotheliogenic potency of the commercially valu able forms of asbestos, assuming equal exposures, is crocidoiite > amosite > chrysotile. However, this ranking is based on the assumption of equal exposures, which in fact was not the case for asbestos workers in the United States in the past decades, as pointed out by Hughes and Weill. Our data indicate that exposures to amosite and jncmolitedcontaminated chrysotile were much greater among these work- e. Hence, the ranking of importance of fiber type in production of mesothelioma among these workers is different from the ranking of fiber potency. We thank Drs. Hughes and Weill for clarifying this point. _Our conclusions regarding the approximately equal importance of chrysotile and crocidoiite in the production of mesotheliomas in the United States is based on two assumptions implied in our article: 1) it is mainly fibers 5 pm or greater in length that are important in the pathogenesis of mesothelioma, and 2) it is the fibers that accumulate in the lung that are responsible for disease [Wagner and EooleyF-198ft Churg, 1988]. Since approximately equal numbers ofchrvsotjj^nd<cl^idqllite fiberjp with these dimensional characteristics were found in our study, it foIIowsTroffTtlie above assumptions that these two fiber types. aiBJtf_mughlv.equalJmpQrtance-in.thfi causation a iiomas. This finding also reflects the facts that chrysotile exposure w _ an crocidoiite exposure among U.S. asbestos workers, and that chrysotile (unlike crocidoiite) tends to break down in the lungs into short (<5 pm in length) fibers that are more readily cleared. Some authors have suggested that the disparity in mesotheliogenic potency between chrysotile and crocidoiite may be due to the role of contaminating tremolite as the causative agent in chrysotile-induced mesotheliomas [Churg, 1988; McDonald et al., 1989] since tremolite accounts for no more than 1% of chrysotile dust. However, the recent study by Begin et al. f 19921 indicates that it is by no means clear that tremblife is the causative agent in chrysotile dust-induced mesotheliomas amdng~Quebec miners and miliefs. Address reprint requests to Dr. Victor L. Roggli, Department of Pathology, Box 3712, Duke University Medical Center. Durham, NC 27710. Accepted for publication July 28, 1993. 1994 Wiley-Liss, Inc. 612 Roggli et al. No quantification of fiber concentrations by fiber type was included in our report [Roggii et ah, 1993] so no comparisons with a control or reference population as suggested by Hughes and Weill were possible. We have analyzed fiber types and numbers by scanning electron microscopy in 120 cases of mesothelioma to date. In eight of these cases, asbestos body counts and asbestos fiber counts for each fiber type were not distinguishable from those of our comparison population as previously reported [Roggli, 1991; Roggli et al., 1992]. In about 20% of the cases, there was a concentration of chrysotile fibers 5 p.m or greater in length which exceeded that of our comparison population. However, all of these cases also had elevated levels of commercial amphiboles, and no cases of mesothelioma had elevated levels of chrysotile only. Nonetheless, five cases had elevated levels of tremolite as compared to our reference population in the absence of detectable excesses of either amosite or crocidoiite. These five mesothelioma cases will be reported separately (Srebro and Roggli, in preparation). Thus, although we agree with Drs. Hughes and Weill regarding the distinction between fiber potency vs. fiber importance, we cannot agree that our conclusions regarding chrysotile are unjustified, based on the current study [Roggli et al., 1993] and the unpublished observations noted above. Victor L. Roggli, MD Department of Pathology Durham VA and Duke University Medical Centers Durham, North Carolina _ Philip C. Pratt, MD Department of Pathology Duke University Medical Center Durham, North Carolina 1 Arnold R. Brody, PhD Department of Pathology Tulane School of Public Health and Tropical Medicine New Orleans, Louisiana REFERENCES . B4gin R, Gauthier J-J, Desmeules M, Ostiguy G (1992): Work-related mesothelioma in Qu6bec. 1967 1990. Am J Ind Med 22:531-542. Churg A (1988): Chrysotile, tremolite, and malignant mesothelioma in man. Chest 93:621-628. Hughes JM, Weill H (1994): Potency versus importance in fiber pathogenicity. Am J Ind Med 25:609 610. McDonald JC. Armstrong B. Case B. Doell D, McCaughey WTE, McDonald AD. Sfbastien P (1989): Mesothelioma and asbestos fiber type: Evidence from lung tissue analyses. Cancer 63:1544-1547. Roggli VL (1991): Mineral fiber content of lung tissue in patients with malignant mesothelioma. In Henderson DW, Shiikin KB, LangloisSLP, WhitakerD(eds.): "MalignantMesothelioma." New York: Hemisphere, pp 201-222. Roggli VL. Pratt PC, Brody AR (1992): Analysis of tissue mineral fiber content. In Roggli VL. Green berg SD, Pratt PC (eds): "Pathology of Asbestos-Associated Diseases." Boston: Little. Brown & Co., pp 299-345. Roggii VL, Pratt PC. Brody AR (1993): Asbestos fiber type in malignant mesothelioma: An analytical scanning electron microscopic suidy of 94 cases. Am J Ind Med 23:605-614. Wagner JC. Pooley FD (1986): Mineral fibres and mesothelioma. Thorax 41:161-166. ' r