We are grateful to Dr. Strongosky et al. for confirming that PD may be associated with some but not other cancers. [1] The authors observed several patients with cancers, particularly colon carcinoma, in a large pedigree with the LRRK2 mutation R1441C.
Strongosky et al. also consider the possible relationship between this gene and colon carcinoma and suggest, as we have observed, that the prognosis for these cancers may be favorable. A possible link between PD and cancer might be found in the autophagy-lysosome pathway, which plays a role in both disorders. [4]
Although the role of LRRK2 in cancer is unknown, there are two pathways responsible for cell survival that may involve products of genes associated with PD. These include the mitogen-activated protein kinases (MAPK) (Erk1/2) signaling pathway and the PI3K/Akt dependent pathway. The LRRK2 gene encodes a MAPKKK protein. [5,6] Unraveling the MAPK signal pathway in dopamine neurons and cancer cells may clarify the PD-cancer relationship and open a therapeutic window for cancer as well as PD therapy.
The search for possible co-morbidity between cancers and the PARK8 gene may provide insight into the pathogenesis of both disorders. Since the publication of our paper, two studies have been published supporting our findings. [1] A case-controlled, prospective study of 22,071 US male physicians, followed for 22 years during which time 487 incident cases of PD were identified, showed an inverse relationship between cancers (both smoking-related and non-smoking-related) and the subsequent development of PD. [7]
Another large study in Denmark involving 14,088 patients diagnosed with PD confirmed markedly increased risk for malignant melanoma in this population, but there is no evidence that treatment with levodopa increases the risk. [8]
Unraveling the relationship between PD and cancers is an emerging area of research.
References
4. Pan T, Kondo S, Le W, Jankovic J. The role of autophagy-lysosome pathway in neurodegeneration associated with Parkinson’s disease. Brain 2008 (in press).
5. Deng H, Le W, Guo Y, et al. Genetic analysis of LRRK2 mutations in patients with Parkinson disease. J Neurol Sci. 2006;251:102-106.
6. Tomiyama H, Li Y, Funayama M, et al. Clinicogenetic study of mutations in LRRK2 exon 41 in Parkinson's disease patients from 18 countries. Mov Disord 2006;12:1102-1108.
7. Driver JA, Kurth T, Buring JE, Gaziano JM, Logroscino G. Prospective case-control study of nonfatal cancer preceding the diagnosis of Parkinson's disease. Cancer Causes Control 2007;18:705-711.
8. Olsen JH, Tangerud K, Wermuth L, Frederiksen K, Friis S. Treatment with levodopa and risk for malignant melanoma. Mov Disord 2007;22:1252-1257.
Disclosures: The authors report no conflicts of interest.