• Antibody titer reactogenicity assessment [ Time Frame: up to 12 months ]
  Serum IgG assessment at baseline, after 21 days, 42 days and after 6 months to Pfizer SARS- CoV-2 RNA vaccine in cancer patients under prior or current active antitumor treatment
• Comparison of the immune response in treated and untreated patients [ Time Frame: up to 12 months ]
  Identification of predictive factors for antibody response in treated versus untreated patients

• Safety assessment [ Time Frame: up to 24 months ]
  Number and Grade of Adverse Events (AE) related to vaccine in patients undergoing anti-cancer treatment.
• Antibody titer correlations with therapy [ Time Frame: up to 24 months ]
  To correlate the antibody titer with type and timing of therapy. Particular attention will be devoted to the effect in patients receiving checkpoint inhibitor immunotherapy.
• Antibody titer correlations with cancer [ Time Frame: up to 24 months ]
  To correlate the antibody titer with the type of cancer and cancer staging/grading
• Antibody titer correlations with patients [ Time Frame: up to 24 months ]
  To correlate the antibody titer with host characteristics, including psychological variables such as distress and anxiety or depression.
• Inflammatory response evaluation [ Time Frame: up to 24 months ]
  Dosage of soluble factors (including pro-inflammatory cytokines, Cytokine Multiplex Assay Kits) in responders and non responders to Pfizer SARS-CoV-2 RNA vaccine
• Immune cell activation [ Time Frame: up to 24 months ]
  Correlate soluble factors of inflammatory response with blood cell count and inflammatory and pro-thrombotic biomarkers
• Immunological memory [ Time Frame: up to 24 months ]
  Comparing lymphocyte activation in cancer patients responding to the vaccine versus those non responding (S1/S2 IgG <15 AU/mL)

This is an observational non-interventional study in cancer patients. The study will evaluate the safety, tolerability and immunogenicity of Pfizer SARS-CoV-2 RNA vaccine against COronaVIrus Disease-19 (COVID-19) which will be delivered in the deltoid muscle in 2-dose (separated by 21 days). Blood will be collected in two 5 milliliters (mL) vacuettes for serum Immunoglobulin G (IgG) and Cytokine assessment, at baseline and after 21 days, immediately before the first and the second dose, respectively, then after 42 days from the first dose and finally after 6 months from the baseline. A panel of 22 cytokines (Biorad) will be measured at baseline and after 21 and 42 days in four groups consisting of: no responders (S1/S2 IgG<15 Arbitrary Unit AU/ml at 42 days), slow responders (S1/S2 IgG<15 AU/mL after 21 days and >15 AU/mL after the second dose), fast responders (S1/S2 IgG>15 AU/mL after the first 21 days) and immunized patients (S1/S2 IgG>15 AU/mL at baseline). At baseline, at 42 days and 6 months questionnaires for psychological testing will be dispensed for completion to patients.

After 42 days from the first dose, 15 mL of heparinized peripheral blood from both non-responders (S1/S2 IgG<25 AU/mL) and responders will be used for isolation of different Cluster of Differentiation 4 (CD4+) and CD8+ T cell subpopulations and analysis of their capability to undergo activation/proliferation in response to specific SARS- CoV-2 derived peptides.

• Neoplasms
• Cancer, Treatment-Related

Inclusion Criteria:

• Age ≥18 years
• On treatment for cancer during the last 6 months or being treated >6 months ago but being ultravulnerable
• About to receive "Pfizer-BioNTech COVID-19" vaccine
• Lymphocyte count≥0.5x10^9/L

Exclusion Criteria:

• Subjects who are not eligible for "Pfizer-BioNTech COVID-19" vaccine administration
• Inability and/or unwillingness to sign written informed consent