Ventilator-associated pneumonia (VAP) is a care-related event that could be promoted by immune suppression caused by critical diseases, malignancies and cancer treatments. Low dose of hydrocortisone was proposed for modulation of immune response in the critically ill population. In this monocentric observational study, all cancer patients mechanically ventilated for more than 48 h were included. Effect of low-dose hydrocortisone administered during the first 48 h of mechanical ventilation was evaluated applying inverse probability weighting analysis after propensity score assessment. VAP impact on 1-year mortality, ICU length of stay and mechanical ventilation duration was secondarily determined. Within this cohort, 190 cancer patients were followed. VAP was confirmed in 22.1% of cases in the early hydrocortisone group and confirmed in 42.6% of cases in the no or late hydrocortisone group. Early hydrocortisone exhibited a protective effect on the risk of VAP (OR 0.23; 95% CI 0.12-0.44; P < 0.0001). VAP was associated with 1-year mortality (HR 1.60; 95% CI 1.10-2.34; P = 0.017) and increased ICU length of stay (mean extra length of stay: 4.2 days; 95% CI 0.6-7.8). Immune modulation with low-dose hydrocortisone administered in the first days of mechanical ventilation could protect from VAP occurrence in cancer patients.