Do Age at Diagnosis, Tumour Thickness and Tumour Site Explain Sex Differences in Melanoma Survival? A Sequential Causal Mediation Analysis Using Cancer Registry Data

Background: Previous research has shown that women diagnosed with melanoma have better survival than their male counterparts, but little is known about the underlying mechanisms by which sex affects melanoma survival. Aim: The aim of this study was to quantify the contribution of age at diagnosis, tumor thickness and tumor site to sex differences in 1-year and 5-year melanoma-specific survival. Methods: We conducted a population-based study using cancer registry data including 6,009 men and 5,232 women aged 15-70 years with first primary melanoma diagnosed between 2007 and 2015 in Victoria, Australia. We excluded cases notified via death certificate only. Deaths to the end of 2015 were identified through linkage to the Victorian and national death registries. We decomposed the total effect of sex on melanoma-specific survival into three possible pathways, examining the mediating role of age at diagnosis, tumor thickness and tumor site. The natural indirect effects through the mediators were assessed using weighted, sequential causal mediation analysis. Results: Compared with women, there were 60 (95% confidence interval (CI) 34 to 91) and 201 (95% CI 135 to 267) additional deaths per 10,000 in men within 1 year and 5 years following diagnosis, respectively. Within 1 year following diagnosis, the indirect effect through age at diagnosis was estimated to be 4 (95% CI -2 to 9) additional deaths per 10,000 in men compared with women, explaining 7% of the total effect of sex, while a considerable proportion of the total effect (79%) explained by melanoma thickness [47 (95% CI 32 to 66) additional deaths per 10,000 in men], excluding the potential influence of age at diagnosis on thickness. Similarly, within 5 years after diagnosis, about 13% of the total effect was estimated to be explained by age at diagnosis [26 (95% CI 15 to 38) additional deaths per 10,000 in men] and 86% by tumor thickness [174 (95% CI 142 to 207) additional death per 10,000 in men]. There was no indirect effect through tumor site within 1 year and 5 years postdiagnosis. Conclusion: The lower survival from melanoma of men relative to women appears to be explained primarily by tumor thickness rather than age at diagnosis. Our findings highlight the need for earlier detection of melanoma in men.

Abstract PD2-13: Benefits to breast screening beyond mortality reduction

Background

The value of population-based mammographic screening has been questioned by those who believe that the reduction in mortality from earlier diagnosis is outweighed by harms including overdiagnosis and overtreatment. Much of these commentaries assume that all Early-Stage Breast Cancer (ESBC) is treated the same way after diagnosis; with extensive therapies including surgery, radiotherapy and chemotherapy being standard.

Intensity of treatment received is rarely mentioned in the debate. We hypothesised that those diagnosed through a screening program (Active Screeners (AS)) would receive less extensive surgical treatment and less intense adjuvant therapies than those not recently screened (NRS). If demonstrated, these differences would form an important component of the debate over the role of mammographic screening.

Methods

Retrospective analysis of a consecutive cohort of female patients aged 50-69 and managed for ESBC (invasive or DCIS) during 2007-2013 within a large metropolitan Breast Service, diagnosed either via a population screening program (AS) or outside of the program (NRS). Data on patient characteristics, symptoms, mode of detection, tumour pathology, surgical intervention and adjuvant treatment recommendations were derived from prospectively collected Multi-Disciplinary Meeting (MDM) records. Patients with metastatic disease or prior treatment for breast cancer were excluded.

Results

791 cases were identified (569 with screen-detected cancer, 53 with interval cancers and 169 cancers diagnosed in women not recently screened). Invasive cancers in the AS group were much smaller than in the NRS group – mean 17mm versus 26mm. The AS group had lower grade invasive cancer – grade 1, 2 and 3 were 27%, 42%, 31% - compared with 10%, 39% and 52% in the NRS group. The AS group were more likely to have ER+ve cancers (88% vs 80%) and less likely to have nodal involvement (26% vs 48%). For invasive breast cancer, the NRS group were more than twice as likely to undergo mastectomy than cancers in the AS group (35% vs 16%). Axillary dissections were more common in the NRS than the AS group (43% vs 19%). Adjuvant chemotherapy was recommended more frequently for the NRS group compared to the AS group (65% vs 37%), as was post mastectomy radiotherapy (58% vs 39%). Endocrine therapy was less often recommended to the NRS group (86% versus 77%).

Conclusion

Women diagnosed with early stage breast cancer who are participating in a population based screening program are less likely to receive mastectomy and/or axillary dissection, less likely to receive adjuvant chemotherapy and less likely to receive post-mastectomy radiotherapy. These differences in treatment intensity should be considered in the debate surrounding mammographic screening.

Citation Format: Elder KJ, Nickson C, Cooke S, Machalek D, Rose A, Mou A, Collins JP, Park A, De Boer R, Phillips C, Pridmore V, Farrugia H, Mann GB. Benefits to breast screening beyond mortality reduction [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr PD2-13.

Monitoring interval cancers in an Australian mammographic screening programme

OBJECTIVE

To report the interval cancer rate for BreastScreen Victoria.

DESIGN

Electronic linkage of Breast Screen Victoria records with those of the Victorian Cancer Registry. Interval cancers were expressed as a proportion of the underlying incidence (proportional incidence), and the sensitivity as the number of screen detected invasive breast cancers divided by the total number of invasive breast cancers diagnosed in the screening interval.

SETTING

Victoria, Australia where biennial screening is provided to women aged 40 and older.

SUBJECTS

Victorian women aged 40-79 who attended first round screening in 1994 (103,023 women) and 1995 (107,057 women).

RESULTS

The sensitivity of screening mammography for the two year interval increased with age (p for trend < 0.001) and was 49.4% in women aged 40-49, 68.6% in 50-59 year old women, 80.7% in 60-69 year old women, and 85.2% in women aged 70-79. The proportional incidence in the first year after screening was 59% in 40-49 year old women and 27% in women aged 50-69. In the second year the proportional incidence was 93% in 40-49 year old women and 54% in women aged 50-69.

CONCLUSIONS

Interval cancers comprise such a large proportion of the expected number of cancers in 40-49 year old women that the benefit of screening is likely to be low. For women aged 50-69, the proportional incidence found in this study was similar to those found in the UK programmes.

Childhood cancer in Victoria, Australia, 1970-1989

The incidence of cancer between 1970 and 1989 in children aged less than 15 years and resident in the state of Victoria, Australia, was ascertained using records held by the Victorian Cancer Registry. Altogether, 1,189 children in the 1970s and 1,261 children in the 1980s were registered with new diagnoses of cancer and these were followed up until 30 June 1993. Between 1970-1979 and 1980-1989 the incidence of childhood cancer rose by 14%, but this was not statistically significant. Part of this apparent increase may have been due to improved registration of cases in the 1980s, particularly of certain tumour types, and of tumours in older children who may have been treated outside the major paediatric treatment centres. Between the 2 decades, 5-year survival increased from 49% to 67%, with improvements in almost all tumour types. Only in Ewing's sarcoma did survival proportions decrease, and this may be related to histological misclassification and to an increased proportion of Ewing's arising in the pelvis during the 1980s. There is evidence already that with new treatment regimens introduced during the 1980s survival in the 1990s will show increased gains.

Primary tumors of the brain, cranial nerves and cranial meninges in Victoria, Australia, 1982-1990: patterns of incidence and survival

This report presents for the first time a detailed analysis of the distribution of primary brain tumors in a population in Australia. Data on 3,575 cases of benign and malignant tumors of the brain, cranial nerves and cranial meninges diagnosed among residents of the state of Victoria from 1982 to 1990 are used to calculate incidence rates and survival by histologic type, age and sex and to compare incidence of birthplace, socioeconomic status and year of diagnosis. No sharp decline in incidence rates is seen among those over age 60 and only small increases in incidence over the 9-year period have been observed. The overall incidence rates, distributions by histologic type, and patterns of excess incidence among those born in Southern and Eastern Europe and the Middle East are similar to observations in other geographic areas. No clear trend relating incidence and socioeconomic status is observed. Survival after brain tumor diagnosis is better among women then men (52 vs. 37% survive 5 years); this difference is attributable to the greater frequency among men of the more aggressive tumor types. The most striking male over female excess is for medulloblastoma, a type that occurs predominantly in the pediatric age group. This excess coupled with the fact that this tumor occurs at a much younger age in males may suggest the presence of a genetic predisposition in some patients with this disease.