The crossroads of multiple sclerosis and cancer: Urgent call for clinical direction

Dear Editor,

The co-occurrence of cancer and multiple sclerosis (MS) presents a complex challenge that significantly impacts patient’s quality of life and health outcomes. ¹ Cancer ranks the second or third leading cause of death in this population, closely following the primary burden of MS. Colorectal, breast, and cervical cancers exhibit the highest incidence rates. ² Moreover, the overall survival of these patients is notably reduced.^1,2

Disease-modifying therapies (DMTs) for MS are the standard of care; however, their use is associated with concerns regarding potential malignancies and tumours. Since their introduction into clinical practice, there has been an ongoing effort to assess the extent of the cancer risk linked to DMTs. It has been observed that the incidence of cancer in the MS population has increased since the introduction of these medications. ³

Nonetheless, despite our understanding of the coexistence of these conditions, and the expectation that this trend may increase, there remains a significant gap in our approach: how should we manage DMT treatment in the MS population after a cancer diagnosis?

This issue became acutely relevant when we encountered a recent case involving a woman diagnosed with MS and breast cancer. She was receiving biologic DMT and adjuvant chemotherapy (CTx). It was surprising to find that major Scientific Societies and Academies, including the European and American Academies of Neurology and the Spanish Society, do not offer guidance on the management, monitoring, or clinical course of MS treatments in patients simultaneously dealing with cancer.

Upon reviewing the literature, we found only two recent retrospective studies.^4,5 The first, focused on the clinical course of MS in patients with breast cancer and their experiences dealing with both conditions. ⁴ Authors highlighted concerns raised by neurologists and oncologists regarding the concurrent use of immunosuppressive and anticancer therapies. Furthermore, distinguishing between MS relapses and symptoms resulting from neurological toxicity of the CTx and/or immunotherapy, proved challenging.

The other study, ⁵ described the clinical course of 16 patients with central nervous system (CNS) tumours and MS. They reported that 25% patients discontinued the MS treatment after oncological diagnosis and 31% never initiated it. MS disease activity events mainly occurred in patients not treated with CTx for CNS tumours, likely due to the immunosuppressive mechanisms of CTx.

Furthermore, there remain several unresolved issues concerning immune checkpoints inhibitors (ICIs) used to treat cancer. ⁶ First, it is unclear how ICIs might impact MS outcomes, as immunotherapy engages the immune system to generate antitumour response which runs counter to the purpose of DMTs. This raises concerns about the potential worsening of neurological conditions with ICIs, which can vary by ICIs type. ⁶ Moreover, DMTs might block the mechanism of action of ICIs, potentially reducing its efficacy.

When an MS patient is diagnosed with cancer, it is imperative for neurologists to familiarize themselves with the planned oncological treatment. Close collaboration with other clinical professionals; oncologists and hospital pharmacists, is essential to navigate the complex landscape of managing both conditions effectively.

From an institutional perspective, it is evident that we have yet to address the reality of these patients in our clinical practices. Actual clinical management is currently determined by individual experience of physicians, as there is a lack of comprehensive guidelines or recommendations.

Addressing this issue is of paramount importance. Despite the uncertainties, it is crucial that all professionals involved in the care of these patients collectively address this challenge and provide guidance for the management of DMTs for MS in individuals also contending with cancer.