Tumor diagnosis preceding Parkinson's disease: A case-control study

Longitudinal study of the inverse relationship between Parkinson's disease and cancer in Korea

Despite growing epidemiological evidence, the relationship between Parkinson's disease (PD) and cancer has not been conclusively demonstrated, and related studies are scarce in the Asian population. We aimed to determine the association between PD and subsequent development of various cancers from longitudinal data of a representative sample of Korean adults aged ≥40 years. We retrospectively identified 8381 patients diagnosed with PD from 2002 to 2019 using claims data among 514,866 people of random samples from the Korean National Health Insurance database. We sampled 33,524 age-, sex-, income-, and residential area-matched participants without PD from the same database. The longitudinal associations between PD and overall cancer, as well as 10 common types of cancer, were estimated using multivariable Cox proportional-hazards regression analysis. The adjusted hazard ratio (aHR) of all cancer types was 0.63 (95% confidence interval = 0.57-0.69) in patients with PD compared with matched controls. The aHRs of gastric, thyroid, colorectal, lung, hepatic, and pancreatic cancer and hematological malignancy were 0.69 (0.56-0.85), 0.60 (0.39-0.93), 0.56 (0.44-0.70), 0.71 (0.58-0.84), 0.64 (0.48-0.86), 0.37 (0.23-0.60), and 0.56 (0.36-0.87), respectively. The associations of bladder, gallbladder and biliary duct, and kidney cancer with PD were not statistically significant. Our findings show inverse associations between overall cancer and most cancer types in patients with PD. These inverse associations and their pathogeneses merit further investigation.

Vitamin D and Parkinson's Disease

Vitamin D is a fat-soluble secosteroid, traditionally considered a key regulator of bone metabolism, calcium and phosphorous homeostasis. Its action is made possible through the binding to the vitamin D receptor (VDR), after which it directly and indirectly modulates the expression of thousands of genes. Vitamin D is important for brain development, mature brain activity and associated with many neurological diseases, including Parkinson’s disease (PD). High frequency of vitamin D deficiency in patients with Parkinson’s disease compared to control population was noted nearly twenty years ago. This finding is of interest given vitamin D’s neuroprotective effect, exerted by the action of neurotrophic factors, regulation of nerve growth or through protection against cytotoxicity. Vitamin D deficiency seems to be related to disease severity and disease progression, evaluated by Unified Parkinson’s Disease Rating Scale (UPDRS) and Hoehn and Yahr (H&Y) scale, but not with age of PD onset and duration of disease. Additionally, fall risk has been associated with lower vitamin D levels in PD. However, while the association between vitamin D and motor-symptoms seems to be possible, results of studies investigating the association with non-motor symptoms are conflicting. In addition, very little evidence exists regarding the possibility to use vitamin D supplementation to reduce clinical manifestations and disability in patients with PD. However, considering the positive balance between potential benefits against its limited risks, vitamin D supplementation for PD patients will probably be considered in the near future, if further confirmed in clinical studies.

Parkinson's disease and cancer: a systematic review and meta-analysis of over 17 million participants

OBJECTIVE

To systematically review and qualitatively evaluate epidemiological evidence on associations between Parkinson's disease (PD) and cancer via meta-analysis.

DATA SOURCES

MEDLINE via PubMed, Web of Science and EMBASE, until March 2021.

STUDY SELECTION

Included were publications that (1) were original epidemiological studies on PD and cancer; (2) reported risk estimates; (3) were in English. Exclusion criteria included: (1) review/comments; (2) biological studies; (3) case report/autopsy studies; (4) irrelevant exposure/outcome; (5) treated cases; (6) no measure of risk estimates; (7) no confidence intervals/exact p values and (8) duplicates.

DATA EXTRACTION AND SYNTHESIS

PRISMA and MOOSE guidelines were followed in data extraction. Two-step screening was performed by two authors blinded to each other. A random-effects model was used to calculate pooled relative risk (RR).

MAIN OUTCOMES AND MEASURES

We included publications that assessed the risk of PD in individuals with vs without cancer and the risk of cancer in individuals with vs without PD.

RESULTS

A total of 63 studies and 17 994 584 participants were included. Meta-analysis generated a pooled RR of 0.82 (n=33; 95% CI 0.76 to 0.88; p<0.001) for association between PD and total cancer, 0.76 (n=21; 95% CI 0.67 to 0.85; p<0.001) for PD and smoking-related cancer and 0.92 (n=19; 95% CI 0.84 to 0.99; p=0.03) for non-smoking-related cancer. PD was associated with an increased risk of melanoma (n=29; pooled RR=1.75; 95% CI 1.43 to 2.14; p<0.001) but not for other skin cancers (n=17; pooled RR=0.90; 95% CI 0.60 to 1.34; p=0.60).

CONCLUSIONS

PD and total cancer were inversely associated. This inverse association persisted for both smoking-related and non-smoking-related cancers. PD was positively associated with melanoma. These results provide evidence for further investigations for possible mechanistic associations between PD and cancer.

PROSPERO REGISTRATION NUMBER

CRD42020162103.

The Links between Parkinson's Disease and Cancer

Epidemiologic studies indicate a decreased incidence of most cancer types in Parkinson’s disease (PD) patients. However, some neoplasms are associated with a higher risk of occurrence in PD patients. Both pathologies share some common biological pathways. Although the etiologies of PD and cancer are multifactorial, some factors associated with PD, such as α-synuclein aggregation; mutations of PINK1, PARKIN, and DJ-1; mitochondrial dysfunction; and oxidative stress can also be involved in cancer proliferation or cancer suppression. The main protein associated with PD, i.e., α-synuclein, can be involved in some types of neoplastic formations. On the other hand, however, its downregulation has been found in the other cancers. PINK1 can act as oncogenic or a tumor suppressor. PARKIN dysfunction may lead to some cancers’ growth, and its expression may be associated with some tumors’ suppression. DJ-1 mutation is involved in PD pathogenesis, but its increased expression was found in some neoplasms, such as melanoma or breast, lung, colorectal, uterine, hepatocellular, and nasopharyngeal cancers. Both mitochondrial dysfunction and oxidative stress are involved in PD and cancer development. The aim of this review is to summarize the possible associations between PD and carcinogenesis.

Association between Parkinson's Disease and Risk of Cancer: A PRISMA-compliant Meta-analysis

Previous studies exploring associations between Parkinson's disease (PD) and cancer risks provided controversial results. We conducted this study to examine the association between PD and cancer risks among different cancer types in worldwide populations. We searched for articles published before August 2019 in databases PubMed, Web of Science, EMBASE, Medline, and Google Scholar. The multivariate odds ratio (OR)/relative risk (RR) and 95% confidence intervals (CI) were computed to explore associations between PD and risks of different types of cancers. The present study indicated significantly negative associations between PD and risks of all types of cancers, digestive system cancers, lung cancers, and urinary system cancers. Additionally, no significant associations were shown between PD and risks of breast cancers, reproductive system cancers, or hematological malignancies. The study showed significantly positive associations between PD and risks of skin cancers and brain cancers. In conclusion, our investigation showed that PD patients showed reduced overall cancer risk and reduced risk of some types of cancers (digestive system cancers, lung cancers, and urinary system cancers). We need further studies to explore the underlying mechanism of the association between PD and cancers.

Cancers Preceding Parkinson's Disease after Adjustment for Bias in a Danish Population-Based Case-Control Study

Cancer patients are at lower risk of developing Parkinson's disease (PD) compared with the general population. One explanation is the negative association between smoking and PD, but PD risk is also lower for cancers not related to smoking. Another explanation is survival bias where death from cancer may act as a competing risk. We conducted a large population-based case-control study in Denmark and investigated whether cancer diagnosis reduced the risk of developing PD even after adjusting for important risk factors including smoking, physical activity, and lifetime oestrogen status. Using probabilistic bias analysis we quantified the influence of survival bias. We estimated negative point estimates (ORs) between cancers and PD for all cancers except skin, female breast, and ill-defined and unspecified 0.85 (95% CI 0.59-1.21); smoking-related cancers 0.75 (95% CI 0.45-1.23); and cancers not related to smoking 0.82 (95% CI 0.49-1.38) that are very similar to those previously reported for a much larger Danish register only based study, even though our confidence intervals include the null. These effect estimates shifted towards the null after accounting for survival bias but most bias-adjusted ORs remained below 1 within the range of priors considered in simulations. Overall, cancer patients have a lower risk of developing PD even after controlling for cancer-related lifestyles factors and correcting for survival bias.

Rare variants analysis of cutaneous malignant melanoma genes in Parkinson's disease

A shared genetic susceptibility between cutaneous malignant melanoma (CMM) and Parkinson's disease (PD) has been suggested. We investigated this by assessing the contribution of rare variants in genes involved in CMM to PD risk. We studied rare variation across 29 CMM risk genes using high-quality genotype data in 6875 PD cases and 6065 controls and sought to replicate findings using whole-exome sequencing data from a second independent cohort totaling 1255 PD cases and 473 controls. No statistically significant enrichment of rare variants across all genes, per gene, or for any individual variant was detected in either cohort. There were nonsignificant trends toward different carrier frequencies between PD cases and controls, under different inheritance models, in the following CMM risk genes: BAP1, DCC, ERBB4, KIT, MAPK2, MITF, PTEN, and TP53. The very rare TYR p.V275F variant, which is a pathogenic allele for recessive albinism, was more common in PD cases than controls in 3 independent cohorts. Tyrosinase, encoded by TYR, is the rate-limiting enzyme for the production of neuromelanin, and has a role in the production of dopamine. These results suggest a possible role for another gene in the dopamine-biosynthetic pathway in susceptibility to neurodegenerative Parkinsonism, but further studies in larger PD cohorts are needed to accurately determine the role of these genes/variants in disease pathogenesis.

Prospective comorbidity-matched study of Parkinson's disease and risk of mortality among women

BACKGROUND

Individuals with Parkinson's disease (PD) may have an increased risk of overall mortality compared to the general population. Women may have lower mortality rates from PD than men; however, studies among women on the effect of PD on mortality have been limited and may not have adequately controlled for confounding by comorbidities.

METHODS

We conducted a matched cohort study among participants in the Women's Health Study. 396 incident PD cases were identified through self-report. Each PD case was matched by age to a comparator who was alive and had the same modified Charlson comorbidity score as the PD case. The PD cases and matched comparators were followed for all-cause mortality. Cox proportional hazards models adjusted for age at the index date, smoking, alcohol consumption, exercise and body mass index were used to determine the association between PD and mortality.

RESULTS

During a median of 6.2 years of follow-up, 72 women died (47 PD cases and 25 comparators). The multivariable-adjusted HR for mortality was 2.60 (95% CI 1.56 to 4.32).

CONCLUSIONS

PD was associated with more than a twofold increased risk of all-cause mortality among women. Results are similar to those observed among men.

Associations between cancer and Parkinson's disease in U.S. elderly adults

BACKGROUND

Several studies suggest that cancer is reduced before and after a Parkinson's disease (PD) diagnosis. However, determining relationships among diseases of ageing is challenging due to possible biases in ascertaining disease. This study evaluates the PD and cancer relationship, addressing potential biases.

METHODS

Using Surveillance, Epidemiology, and End Results-Medicare linked data (1992-2005) of adults ≥ 65 years, we assessed PD risk after cancer comparing PD in 743 779 cancer patients with PD in a non-cancer group (n = 419 432) in prospective cohort analyses. We also conducted a case-control study of 836 947 cancer cases and 142 869 controls to assess cancer following PD. We applied Cox proportional hazards models to estimate hazards ratios (HRs) for PD after cancer and unconditional logistic regression to estimate odds ratios (ORs) for PD preceding cancer, controlling for physician visits and other factors. To explore biases in ascertaining cancer, we examined relationships between cancer and automobile accident injuries, which we expected to be null.

RESULTS

No association was observed between cancer and subsequent PD [HR = 0.97; 95% confidence interval (CI) = 0.92-1.01] nor between cancer and subsequent automobile injuries (HR = 1.03; 95% CI = 0.98-1.07). One site, lung cancer, was associated with subsequent reduced PD, which may reflect confounding by smoking. In the case-control analysis, PD was associated with reduced subsequent cancer, overall (OR = 0.77; 95% CI = 0.71-0.82) and for several cancer sites. However, the automobile injury/ subsequent cancer association was similar (OR = 0.83; 95% CI = 0.78-0.88), suggesting a cancer detection bias after serious health outcomes.

CONCLUSIONS

In totality, our data do not support a biological relationship between PD and cancer.

The link between Parkinson's disease and breast and prostate cancers: A meta-analysis

PURPOSE

Clinical observations have shown an increased morbidity for breast cancer or prostate cancer in patients with Parkinson's disease (PD), however, other reports have noted contradictory results. This pooled analysis was utilized to test whether PD is associated with the risk of breast or prostate cancer.

METHODS

We searched PubMed, Embase and Cochrane library and conducted a meta-analysis to clarify the correlation of PD with breast and/or prostate cancer risk. We identified 16 eligible articles from which odds ratios with 95% confident intervals were assessed as main measures in the pooled estimation. Subgroup analyses and cumulative meta-analysis were also performed.

RESULTS

Our results showed no PD risk associated with breast or prostate cancer in the overall population, which was supported by the results of cumulative meta-analyses. The subgroup analyses suggested no significant risk of breast or prostate cancer in patients with PD within relevant subsets, i.e. gender, ethnicity, PD diagnosis time or study design. No evidence of publication bias was observed across the involved studies.

CONCLUSIONS

This meta-analysis indicates a lack of association between PD and risk of breast or prostate cancer.

Morbidity in early Parkinson's disease and prior to diagnosis

BACKGROUND

Nonmotor symptoms are probably present prior to, early on, and following, a diagnosis of Parkinson's disease. Nonmotor symptoms may hold important information about the progression of Parkinson's disease.

OBJECTIVE

To evaluated the total early and prediagnostic morbidities in the 3 years before a hospital contact leading to a diagnosis of Parkinson's disease.

METHODS

Retrospective morbidity data from Danish National Patient Registry records (1997-2007) of 10,490 adult patients with a secondary care diagnosis of Parkinson's disease were compared with 42,505 control cases.

RESULTS

Parkinson's disease was associated with significantly higher morbidity rates associated with conditions in the following categories: mental and psychiatric, nervous system, gastrointestinal, musculoskeletal system and connective tissue, genitourinary, abnormal clinical and laboratory findings, injury, poisoning and certain other external causes, and other factors influencing health status and contact with health services. It was negatively associated with neoplasm, cardiovascular, and respiratory diseases.

CONCLUSIONS

Patients with a diagnosis of Parkinson's disease present significant differences in morbidities early on, following, and prior to, their diagnosis, compared with healthy controls.

Malignant melanoma, breast cancer and other cancers in patients with Parkinson's disease

Previous studies report an atypical cancer pattern among patients with Parkinson's disease. Here, we evaluate the cancer pattern among people diagnosed with Parkinson's disease in an extension of our previous cohort study. For this Danish population-based cohort study, we identified 20,000 people with Parkinson's disease diagnosed in 1977-2006, from the National Danish Hospital Register. Cohort members were followed up for cancer in the Danish Cancer Registry until December 31, 2008, and their incidence rates of cancer were compared to age-, sex- and calendar period-specific rates in the general population as standardized incidence rate ratios (SIRs). In subanalyses, we estimated the risk for cancer among patients with early onset Parkinson's disease and we also compared breast tumor characteristics among women with Parkinson's disease to that of a control group. The overall cancer risk in our cohort was decreased [SIR = 0.86; 95% confidence interval (CI) = 0.83-0.90], as were those for smoking-related (SIR = 0.65; 95% CI = 0.60-0.70) and nonsmoking-related cancers (SIR = 0.79; 95% CI = 0.71-0.86). The cohort had increased risks for malignant melanoma (SIR = 1.41; 95% CI = 1.09-1.80), nonmelanoma skin cancer (SIR = 1.29; 95% CI = 1.18-1.39) and female breast cancer (SIR = 1.17; 95% CI = 1.02-1.34). Among patients with early onset Parkinson's disease, the risk for cancer was comparable to that of the general population. Of breast tumor characteristics, only grade of malignancy differed between Parkinson's disease women and controls. This study confirms a lower cancer risk among people with Parkinson's disease. Increased risks for malignant melanoma, nonmelanoma skin cancer and breast cancer might be due to shared risk factors with Parkinson's disease.

Epidemiology and etiology of Parkinson's disease: a review of the evidence

The etiology of Parkinson's disease (PD) is not well understood but likely to involve both genetic and environmental factors. Incidence and prevalence estimates vary to a large extent-at least partly due to methodological differences between studies-but are consistently higher in men than in women. Several genes that cause familial as well as sporadic PD have been identified and familial aggregation studies support a genetic component. Despite a vast literature on lifestyle and environmental possible risk or protection factors, consistent findings are few. There is compelling evidence for protective effects of smoking and coffee, but the biologic mechanisms for these possibly causal relations are poorly understood. Uric acid also seems to be associated with lower PD risk. Evidence that one or several pesticides increase PD risk is suggestive but further research is needed to identify specific compounds that may play a causal role. Evidence is limited on the role of metals, other chemicals and magnetic fields. Important methodological limitations include crude classification of exposure, low frequency and intensity of exposure, inadequate sample size, potential for confounding, retrospective study designs and lack of consistent diagnostic criteria for PD. Studies that assessed possible shared etiological components between PD and other diseases show that REM sleep behavior disorder and mental illness increase PD risk and that PD patients have lower cancer risk, but methodological concerns exist. Future epidemiologic studies of PD should be large, include detailed quantifications of exposure, and collect information on environmental exposures as well as genetic polymorphisms.

Inflammatory mechanisms of neurodegeneration in toxin-based models of Parkinson's disease

Parkinson's disease (PD) has been associated with exposure to a variety of environmental agents, including pesticides, heavy metals, and organic pollutants; and inflammatory processes appear to constitute a common mechanistic link among these insults. Indeed, toxin exposure has been repeatedly demonstrated to induce the release of oxidative and inflammatory factors from immunocompetent microglia, leading to damage and death of midbrain dopamine (DA) neurons. In particular, proinflammatory cytokines such as tumor necrosis factor-α and interferon-γ, which are produced locally within the brain by microglia, have been implicated in the loss of DA neurons in toxin-based models of PD; and mounting evidence suggests a contributory role of the inflammatory enzyme, cyclooxygenase-2. Likewise, immune-activating bacterial and viral agents were reported to have neurodegenerative effects themselves and to augment the deleterious impact of chemical toxins upon DA neurons. The present paper will focus upon the evidence linking microglia and their inflammatory processes to the death of DA neurons following toxin exposure. Particular attention will be devoted to the possibility that environmental toxins can activate microglia, resulting in these cells adopting a “sensitized” state that favors the production of proinflammatory cytokines and damaging oxidative radicals.

Pro-oncogenic and anti-oncogenic pathways: opportunities and challenges of cancer therapy

Carcinogenesis is the uncontrolled growth of cells gaining the potential to invade and disrupt vital tissue functions. This malignant process includes the occurrence of 'unwanted' gene mutations that induce the transformation of normal cells, for example, by overactivation of pro-oncogenic pathways and inactivation of tumor-suppressive or anti-oncogenic pathways. It is now recognized that the number of major signaling pathways that control oncogenesis is not unlimited; therefore, suppressing these pathways can conceivably lead to a cancer cure. However, the clinical application of cancer intervention has not matched up to scientific expectations. Increasing numbers of studies have revealed that many oncogenic-signaling elements show double faces, in which they can promote or suppress cancer pathogenesis depending on tissue type, cancer stage, gene dosage and their interaction with other players in carcinogenesis. This complexity of oncogenic signaling poses challenges to traditional cancer therapy and calls for considerable caution when designing an anticancer drug strategy. We propose future oncology interventions with the concept of integrative cancer therapy.

Parkinson's disease and cancer risk: a systematic review and meta-analysis

OBJECTIVE

To appraise the existing literature on cancer risk among patients with Parkinson's disease (PD), determine the overall cancer risk ratio among patients with PD, explore reasons for variations in study results, and assess the potential for publication bias.

METHODS

Studies reporting cancer risk in patients with PD were identified by searching electronic databases through 18 November 2009 using the terms PARKINSON DISEASE, NEOPLASM, and CANCER. Reviewers individually performed data extraction and scored each study using a quality assessment instrument. Cancer risk in all patients with PD was calculated overall, and after excluding melanoma and other skin cancers. We tested for heterogeneity and publication bias, and stratified for gender, smoking-related versus non-smoking-related cancers, and study quality. We pooled effect sizes using fixed-effects and random-effects models.

RESULTS

We included 29 studies in the overall analysis for a total of 107,598 patients with PD. Compared to controls, the aggregate risk for cancer in patients with PD was 0.73 (95% confidence interval [CI], 0.63-0.83), and after excluding skin tumors, 0.69 (95% CI, 0.62-0.78). These risks varied by gender (males, RR = 0.71, 95% CI, 0.57-0.88; females, RR = 0.82; 95% CI, 0.68-0.98). After strictly excluding skin tumors, both smoking-related (RR = 0.61; 95% CI, 0.58-0.65) and non-smoking-related cancer rates (RR = 0.76; 95% CI, 0.65-0.89) were significantly lower among patients with PD .

CONCLUSIONS

Studies on cancer risk among patients with PD collectively show significantly reduced cancer risk ratios. Further research to explain the biological mechanisms, particularly for the association with non-smoking-related cancers, appears warranted.

A common biological mechanism in cancer and Alzheimer's disease?

Cancer and Alzheimer's disease (AD) are two common disorders for which the final pathophysiological mechanism is not yet clearly defined. In a prospective longitudinal study we have previously shown an inverse association between AD and cancer, such that the rate of developing cancer in general with time was significantly slower in participants with AD, while participants with a history of cancer had a slower rate of developing AD. In cancer, cell regulation mechanisms are disrupted with augmentation of cell survival and/or proliferation, whereas conversely, AD is associated with increased neuronal death, either caused by, or concomitant with, beta amyloid (Abeta) and tau deposition. The possibility that perturbations of mechanisms involved in cell survival/death regulation could be involved in both disorders is discussed. Genetic polymorphisms, DNA methylation or other mechanisms that induce changes in activity of molecules with key roles in determining the decision to "repair and live"- or "die" could be involved in the pathogenesis of the two disorders. As examples, the role of p53, Pin1 and the Wnt signaling pathway are discussed as potential candidates that, speculatively, may explain inverse associations between AD and cancer.

Genetic determinants of hair color and Parkinson's disease risk

OBJECTIVE

A history of melanoma is associated with increased risks for Parkinson's disease (PD). We examined whether hair color, one of the most important phenotypes of pigmentation and a risk factor for melanoma, was associated with PD risk in the Health Professionals Follow-up Study (HPFS; 1986-2002) and the Nurses' Health Study (NHS; 1980-2002).

METHODS

We included 38,641 men and 93,661 women who were free of PD at baseline. Information on natural hair color in early adulthood (age 18-21 years) was assessed via a questionnaire. We also conducted a case-control study (298 PD cases) nested in these two cohorts to examine the association between the melanocortin1-receptor Arg151Cys polymorphism and PD risk. Relative risks (RRs) were estimated using Cox proportional hazards models in the cohort analyses and conditional logistic regression in the nested case-control study.

RESULTS

PD risk increased with decreasing darkness of hair color. Pooled RRs for PD were 1 (reference), 1.40, 1.61, and 1.93 (95% confidence interval, 1.1-3.4) for black, brown, blond, and red hair, respectively, after adjusting for age, smoking, ethnicity, and other covariates. The associations between hair color and PD were particularly strong for relative younger onset of PD (<70 yr) (adjusted RR for red vs black hair = 3.83; 95% confidence interval, 1.7-8.7). In the case-control study, participants with Cys/Cys genotype, which was associated with red hair, had a greater PD risk, relative to the Arg/Arg genotype (adjusted RR, 3.15; 95% confidence interval, 1.1-9.4).

INTERPRETATION

These findings suggest a potential role of pigmentation in PD.

Natural killer cells of Parkinson's disease patients are set up for activation: a possible role for innate immunity in the pathogenesis of this disease

Neuroinflammation in Parkinson's disease (PD) involves activation of microglia, participation of several inflammatory cytokines, prostaglandins, complement and systemic activation of natural killer (NK) cells, suggesting that innate immunity has a role in the pathogenesis of this disease. In this study, we examined NK activity and the expression of its regulatory molecules in peripheral lymphocytes of PD patients and compared the results with those of healthy controls. Expression of the inhibitory NKG2A receptors was significantly lower in PD, causing PD patients to be susceptible in a condition for NK activation after NK cells bind to target cells via these receptors.

Prospective case–control study of nonfatal cancer preceding the diagnosis of parkinson’s disease

OBJECTIVE

Prior studies suggest a decreased frequency of cancer in patients with Parkinson's disease (PD). We conducted a nested case-control study to estimate the association between the diagnosis of PD and a history of preceding cancer.

METHODS

Our case-control study was nested within a prospective cohort of 22,071 US male physicians. During 22 years of follow-up, 487 incident cases of PD were identified and matched by age to 487 controls. We then evaluated a history of cancer prior to the index date that was confirmed by medical record review.

RESULTS

The frequency of any cancer was less in cases (13.1%) than in controls (14.8%). There was an inverse relationship between overall cancer (odds ratio [OR] = 0.83; 95% CI, 0.57-1.21), smoking-related (OR = 0.74; 95% CI, 0.35-1.57), and non-smoking-related cancer (OR = 0.88; 95% CI, 0.59-1.32) and the subsequent development of PD. Smoking significantly modified the relationship between PD and smoking-related cancer (p (interaction) = 0.002). PD cases who smoked had an OR of 0.32 (95% CI, 0.11-0.89) for smoking-related cancer. In contrast, PD cases who never smoked had an OR of 6.85 (95% CI, 0.83-56.39).

CONCLUSIONS

Our data suggest that the frequency of cancer preceding the diagnosis of PD is decreased. Smoking status prior to PD or cancer diagnosis significantly modified the association between smoking-related cancer and PD.

A Prospective Cohort Study of Cancer Incidence Following the Diagnosis of Parkinson's Disease

BACKGROUND

Prior studies suggest a decreased risk of cancer among patients with Parkinson's disease (PD).

METHODS

Matched cohort analysis among the 22,071 participants in the Physician's Health Study. A total of 487 incident cases of PD without preceding cancer were identified by self-report. Each PD case was matched by age to a reference participant who was alive and cancer free at the time of PD diagnosis. Both cohorts were followed for incident cancer. We used proportional hazards models to calculate adjusted relative risks (RR) for cancer.

RESULTS

A total of 121 cancers were confirmed during a median follow-up of 5.2 years (PD) and 5.9 years (reference). Those with PD developed less cancer (11.0% versus 14.0%), with an adjusted RR of 0.85 [95% confidence interval (95% CI), 0.59-1.22]. Reduced risk was present for smoking-related cancers such as lung (RR, 0.32), colorectal (RR, 0.54), and bladder (RR, 0.68), as well as for most non-smoking-related cancers such as prostate cancer (RR, 0.74). In contrast, PD patients were at significantly increased risk (RR, 6.15; 95% CI, 1.77-21.37) for melanoma. PD patients who smoked were at reduced risk for smoking-related cancer (RR, 0.33; 95% CI, 0.12-0.92), whereas nonsmokers with PD were at increased risk (RR, 1.80; 95% CI, 0.60-5.39). This interaction was statistically significant (P(interaction) = 0.02).

CONCLUSIONS

Our results suggest a decreased incidence of most cancers in patients with PD. PD patients had a significantly increased risk of malignant melanoma, a finding consistent with prior studies. We confirmed an interaction between smoking and the relationship of PD to smoking-related cancer that may fit the pattern of a gene-environment interaction.

Malignant Melanoma and Other Types of Cancer Preceding Parkinson Disease

BACKGROUND

A large follow-up study in Denmark showed a two-fold higher incidence of malignant melanoma in patients with Parkinson disease than in the general population. Using a population-based case-control approach, we investigated the prevalence of malignant melanoma, skin carcinoma, and other cancers before a first hospitalization or outpatient visit for Parkinson disease.

METHODS

We used the national Danish Hospital Register to identify 8090 patients with a primary diagnosis of Parkinson disease during the period of 1986-1998. Each case was matched with 4 population controls selected at random from among inhabitants alive at the date of first hospital contact with the patient. Incident cases of cancer since 1943 were ascertained by linkage to the Danish Cancer Registry, and the cancer histories of patients with Parkinson disease were compared with those of population controls.

RESULTS

We observed an increased prevalence of malignant melanoma and skin carcinoma prior to the first hospital contact for Parkinson disease, with overall odds ratios of 1.44 (95% confidence intervals = 1.03-2.01) and 1.26 (1.11-1.43), respectively. To the contrary, we observed a reduced prevalence of cancers at smoking-related sites in patients before their first hospital contact for Parkinson disease.

CONCLUSIONS

Our finding of an increased prevalence of malignant melanoma and skin carcinoma before the diagnosis of Parkinson disease weakens the suggested hypothesis that these cancers are caused by the treatment of Parkinson disease. The finding of a decreased prevalence of smoking-related cancers preceding Parkinson disease is consistent with the well-known higher risk of Parkinson disease among nonsmokers.

Epidemiology of Parkinson's disease

The causes of Parkinson's disease (PD), the second most common neurodegenerative disorder, are still largely unknown. Current thinking is that major gene mutations cause only a small proportion of all cases and that in most cases, non-genetic factors play a part, probably in interaction with susceptibility genes. Numerous epidemiological studies have been done to identify such non-genetic risk factors, but most were small and methodologically limited. Larger, well-designed prospective cohort studies have only recently reached a stage at which they have enough incident patients and person-years of follow-up to investigate possible risk factors and their interactions. In this article, we review what is known about the prevalence, incidence, risk factors, and prognosis of PD from epidemiological studies.