Due to recent approvals, a significant number of adult cancer patients are undergoing treatment with checkpoint inhibitor antibodies. While these treatments have revolutionized cancer care, they come with inherent risks of toxicities, primarily mediated by the patient's own immune system.

Among the most common side effects are dermatological toxicities, which although generally mild, significantly impact patients' quality of life. These issues are often underdiagnosed and lack proactive interventions. This study aims to demonstrate that proactive measures using Niacinamide and Shea Butter can either prevent or mitigate the severity of these toxicities.

Thus, this study seeks to contribute novel insights into managing patients undergoing active immunotherapy, a field that remains relatively unexplored. Dermocosmetic products used in both armes of this trial are already approved for over-the-counter use, ensuring accessibility without prescription.

Study Hypothesis: The prophylactic use of Niacinamide and Shea Butter in dermocosmetic products reduces the frequency and severity of immune-mediated skin toxicities in cancer patients receiving checkpoint inhibitor antibodies.

This single-center trial will be conducted at Hospital de la Santa Creu i Sant Pau, employing a parallel arm design with randomization overseen by the center's statistician. Participants will be randomly assigned to either arm, with an active control group to monitor dermocosmetic product usage frequency and type. The blinding protocol will be single-blind to ensure unbiased evaluation.

The study aims to assess the incidence of pruritus among adult cancer patients receiving checkpoint inhibitor antibodies, correlating these findings with the efficacy of dermocosmetic products containing Niacinamide and Shea Butter. Additionally, it will evaluate the impact on the quality of life of these patients.

The intervention group will receive soap and an emollient formulated with Shea Butter and Niacinamide, while the control group will use products containing Argan Oil and Coconut Butter. Both groups will undergo a 6-month treatment regimen.

Key endpoints include:

• Skin pruritus
• Relationship between skin condition and quality of life Consecutive non-probabilistic sampling will be used to recruit all patients with solid tumors initiating immunotherapy.

Using GranMo calculator version 7.2 with 95% confidence and a precision of +/- 0.07, the study calculated a sample size of 128 patients. Recruitment will aim for 130 patients to account for potential attrition, split evenly between Arm 1 and Arm 2.

Data analysis will involve importing, cleaning, and recoding variables followed by univariate analysis using IBM SPSS v.25 The study will adhere strictly to international ethical standards for clinical research, including the Declaration of Helsinki and Good Clinical Practice guidelines. Participants will be fully informed about the study's nature, objectives, procedures, potential risks, benefits, and their right to withdraw without impact on their care.

An information/consent form has been designed accordingly. Participants will receive hygiene and hydration products at no cost, though no financial compensation will be provided.

Monitoring, auditing, reviews by the CEIC, and regulatory inspections will be conducted to ensure adherence to protocol and regulatory requirements.

The choice of control treatment aims to replicate real-world conditions while assessing approved products. Participants will be followed for 6 months from informed consent signing.

Inclusion Criteria:

• Adult patient
• Diagnosed with any solid cancer
• Initiating treatment with checkpoint inhibitor antibodies
• Able to speak and understand Spanish and/or Catalan

Exclusion Criteria:

• Unable to sign informed consent
• Unable to comprehend the study for giving consent
• Language barrier: Does not speak or understand Spanish or Catalan