Background: Lymphopenia commonly occurs in cancer patients and predicts poor prognosis. It is caused by radioand chemotherapy, with malnutrition and treatment-related oxidative stress playing key roles in its pathogenesis. Tumour-related morbidity is reported to be associated with reduced plasma ascorbate, which is a key physiological antioxidant and essential factor in immune function. Method: A prospective observational study was conducted on 48 cancer patients with lymphopenia (<1500/μL) to investigate the total lymphocyte count (TLC) during four weeks of elective adjuvant treatment with intravenous (iv) vitamin C 7.5 g (Pascorbin®7.5 g) once a week. TLC values at baseline (just prior to start of treatment) and after 4 weeks treatment were compared using descriptive statistics. Results: After 4 weeks iv vitamin C 7.5 g, TLC increased by a mean of 211/μL (p = 0.0018). Subgroup analyses showed that, in patients with severe lymphopenia (n = 25) (TLC <1000/μL), the increase in TLC was greater with a mean rise of 368/μL (p = 0.0004), than in patients (n = 23) with an initial TLC of 1000-1500 (mean rise of 40/μL) (p = 0.6105). TLC increased by at least 240/μL in half of the patients with severe lymphopenia and by more than 610/μL in 25% of patients. Conclusion: Our data indicate that iv high-dose vitamin C treatment increases TLC, which strongly implies improvement of immune function, especially in patients with severe lymphopenia. Appropriately-powered, randomized, placebo-controlled trials of iv high-dose vitamin C are now needed to define more precisely its role in the treatment of cancer-related lymphopenia and how this impacts on the patients' clinical prognosis.

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