This paper presents 166 individuals with malignant mesothelioma and asbestos exposure through documented use of cosmetic talcum powder. For 122 of 166, their only known exposure to asbestos was their use of cosmetic talcum powder. Without the recognition of asbestos exposure through cosmetic talcum powder, 73.5% of the cases might well have been considered “idiopathic.” Similarly, for those 26.5% of cases with additional asbestos exposure along with the talc, those alternate exposures would have been mistakenly considered as the sole, and sufficient, cause of the mesothelioma. Historically, the attributable risk of asbestos for mesothelioma in women ranged from around 20–50%. However as Baur et al. point out, misclassification or inadequate exposure ascertainment has led to this low attributable risk for women compared to men. . Data from occupationally exposed cohorts that included men and women actually show that compared to similarly exposed men, women had higher mortality rates from mesothelioma [17,18,19,20]. Lacourt found that at low-level cumulative asbestos exposure ((0 – 0.1 f-cc/year) women were more likely to develop mesothelioma than men . Magnani (2008) found the SMR for mesothelioma was higher for women than for men among workers at an asbestos cement plant . Frank et al. (2009) found mesothelioma rates in the Qingdao region of China were correlated with a higher proportion of women employed in asbestos manufacturing industries.  In some instances authors limited the characterization of asbestos exposure in women to certain industries, such as shipbuilding during wartime , thus neglecting other potential sources and decreasing the attributable risk. Conversely, when non-occupational exposures were included for women, even with low-intensity domestic exposure considered, the attributable risk increased from 40% to 64.8% .
Given that all types of asbestos can cause mesothelioma , it is important to consider every source of exposure to asbestos in an individual. Talcum powder has been contaminated with both chrysotile and amphibole asbestos (predominately anthophyllite and tremolite) [8, 25, 26]. Recently, Wong et al. (2021) found significantly elevated risks of mesothelioma among individuals with only chrysotile exposure and for mixed fiber exposure. . Chrysotile alone (OR = 3.8) and in combination with tremolite/anthophyllite asbestos (OR = 3.9) were associated with similar increases in risk of mesothelioma. These three fiber types are most commonly found in cosmetic talc, and given that different ore sources were used in manufacturing over time, it is likely that many formulations and uses of talcum powder involved mixed fiber type exposure. There is no scientific basis to state that one type of exposure was the sole cause of the mesothelioma in a mixed exposure scenario. For example, rates of mesothelioma have been evaluated based on either job type or locale (e.g., construction, shipping) rather than on each specific task or exposure within the job category. Furthermore, mesothelioma is a disease that occurs following a long latency period. It is important to consider whether the latency period for all exposures, whether due to asbestos in talcum powder, or through occupational or para-occupational exposures meets the minimum latency period.
Subgroups of individuals not traditionally known to be exposed to asbestos have been identified, such as teachers. In this case series, 12 teachers (7.2% of cases) were diagnosed with mesothelioma. Anderson et al. identified 12 school teachers with mesothelioma in Wisconsin (6 male, 6 female). . Nine cases had no known exposure to asbestos, although several worked in school buildings with asbestos containing building materials (ACBM) present, but the condition of the ACBR while the teachers were present in the school was unknown. No history of talcum powder use was elicited. Marianaccio et al. identified mesotheliomas in 11 female teachers in Italy. . Mazurek et al. evaluated mesothelioma deaths in women in the United States from 1999–2020 using death certificate data. . Mesothelioma was noted in 32 female elementary and middle school teachers. No information on exposure to asbestos or specific tasks at work or a comprehensive exposure history was available; no history of talcum powder use was elicited, as the study was based solely on death certificates. Tomasallo et al. found increased mortality among school teachers in Wisconsin, USA. . They noted that para-occupational or take home exposure could be responsible for the increased risk. Again, no history of asbestos exposure through talcum powder usage was ascertained. It might be possible that exposure to ACBM played some role in these mesotheliomas, however, the notable history of exposure to asbestos-containing talcum powders among teachers in this case series, highlights the importance of assessing this source of exposure in future studies of mesothelioma in teachers and other predominantly female professions.
Mazurek et al. found seven cases of mesothelioma among female hairdressers. . Our series identified five hairdressers/barbers with documented occupational exposure to asbestos containing talcum powder. Moline et al. found three hairdressers who used cosmetic talc as part of their occupation,  and Emory et al.  found 4 hairdressers out of 75 patients. Pavlisko et al. identified a hairdresser in their study of mesothelioma in women, but classified the case in the non-occupational/paraoccupational exposure category.  McDonald attributed the finding of tremolite in the lung tissue of a chrysotile worker to his prior occupational exposure to talc as a barber . Rodelsberger recognized talc as a source of asbestos exposure and identified hairdressers and barbers as asbestos-exposed industries . The examples of these two occupational subgroups, teachers with personal use of cosmetic talc, and hairdressers with occupational use of cosmetic talc, show the importance of obtaining a thorough history and determining all potential sources of asbestos exposure.
This case series describes mesotheliomas in end-users of cosmetic talcum powder, thus using no personal protective equipment or dust suppression activities, unlike some cohorts with occupational exposures . Prior mortality studies of talc miners and millers in Italy (and other countries) have not identified mesotheliomas in their populations, although two cases of peritoneal cancer were identified by Pira et al. . The Rubino, Coggiola and Pira et al. studies used mortality data collected prior to an ICD mesothelioma code, which could impact proper classification of mesothelioma. [35,36,37]. The studies had a relatively small sample size, which given the rarity of mesothelioma, even among highly exposed individuals, would have led to insufficient statistical power . Fordyce studied Vermont talc miners and found two mesotheliomas in the small cohort of 427 miners; Vermont talc has been used in cosmetic talcum powder .
Fiber burden studies were done in some individuals from the two prior case series of mesothelioma among individuals with cosmetic talcum powder use. Moline et al. reported on tissue fiber analysis in six of 33 individuals. Asbestos fibers, of the types found in cosmetic talc, were found in all six samples. Emory et al. found anthophyllite asbestos in all 9 individuals for whom tissue fiber analysis was done. Tremolite was found in six of the cases in addition to the anthophyllite. Hull et al.  looked at New York State talc miners and found anthophyllite, tremolite/actinolite, chrysotile and talc in their lungs. There were over a dozen cases of mesothelioma identified in these talc miners. Our case series did not include data on tissue sampling, which is not typically done for clinical purposes; rather we relied on patient history. For occupational exposures to asbestos, fiber analysis is not required to ascertain a history of exposure, rather the history of exposure to asbestos is sufficient . This should be no different for environmental exposures, such as asbestos exposure in cosmetic talcum powder, or even para-occupational exposures.
Pleural mesothelioma is more common than peritoneal mesothelioma , with estimates of pleural mesothelioma occurring approximately 80–90% of the time compared to peritoneal mesothelioma. The presenting location for the tumor, either pleural or peritoneal, was similar in all three recent case series. In Moline et al., 11 of 33 patients had peritoneal mesothelioma and in Emory et al., 23 of 75 cases were peritoneal mesothelioma. In this larger case series, the proportion of peritoneal mesotheliomas was 31.3%. The proportion of men in each of the three case series was similar. In Emory et al., 15% of the cases were men, compared with 18% of the cases in Moline et al. In the current case series, among 122 cases with talc-only exposure, 20.5% were men, slightly above the proportion in two previous case series. This might reflect growing awareness among men that talcum powder use could explain their mesothelioma, particularly when no other identifiable source of asbestos was identified. Few individuals in this case series underwent testing for the tumor suppressor gene, BAP-1, which is associated with an increased risk for mesothelioma when associated with asbestos exposure,  including greater susceptibility at low doses of asbestos such as exposures from cosmetic talcum powder use. Interestingly, there was a greater frequency of peritoneal mesothelioma cases in those with the BAP-1 mutation and asbestos exposure .
Several authors have written about the importance of the cumulative dose, which has been related to several asbestos-caused diseases, both non-malignant and non-malignant. Luberto et al. discussed the “increased mortality risk due to asbestos exposure for malignant neoplasm of pleura, peritoneum, lung and ovary, as well as asbestosis, all increasing with cumulative exposure.”  Henderson et al. commented on the use of the cumulative exposure model in the Helsinki Criteria.  Iwastsubo and colleagues, citing only low exposures leading to disease noted that “excess of mesothelioma was observed for levels of cumulative exposure.”  Ferrante and her colleagues  found that the “risk of pleural malignant mesothelioma increased with cumulative asbestos exposure and also in analyses limited to subjects non-occupationally exposed,” comparable to the current case series. Albin et al.  even noted that “colorectal cancer displayed a clear relation with cumulative dose,” as one would reasonably expect with asbestos-related diseases.
This case series may reflect the potential sources of bias that impact all studies that use cases in which litigation is occurring. However, because mesothelioma is a rare disease and full environmental histories are rarely obtained or documented, it would be impossible to amass so many cases with one type of exposure using standard sources such as hospital or cancer registry records. Furthermore, most patients (and their clinicians) are unaware of the presence of asbestos in talcum powder, leading them to report no known asbestos exposure. The data related to years of exposure to cosmetic talcum powder was obtained and typically described in great detail during sworn testimony. For nearly one-quarter of the individuals in this series, additional exposures to asbestos were reported along with the cosmetic talcum powder. When available, information regarding talcum powder usage was corroborated by sworn testimony of family members. Typically, the questioning of individuals about alternate exposures to asbestos as part of litigation is fairly comprehensive, but it is possible that there were additional, unknown sources. This presents a challenge for any study of asbestos exposure and, in particular, mesothelioma, given the long latency period from the onset of exposure to the development of disease.