Oncologists face challenges in the management of SARS-CoV-2 infections and post-SARS-CoV-2 cancer treatment. We analyzed diagnostic, clinical and post-SARS-CoV-2 scenarios in patients from three German cancer centers with RT-PCR confirmed SARS-CoV-2 infection. Sixty-three patients with SARS-CoV-2 and hematologic or solid neoplasms were included. Thirty patients were initially asymptomatic, 10 of whom developed COVID-19 symptoms subsequently. Altogether 20 (32%) patients were asymptomatic, 18 (29%) had mild, 12 (19%) severe and 13 (20%) critical courses. Lymphocytopenia increased risk of severe/critical COVID-19 three-fold (p = 0.015). Asymptomatic course was not associated with age, remission status, therapies or co-morbidities. Secondary bacterial infection accompanied more than one third of critical COVID-19 cases. Treatment was delayed post-SARS-CoV-2 in 46 patients, 9 of whom developed progressive disease (PD). Cancer therapy was modified in 8 SARS-CoV-2 survivors because of deteriorating performance or PD. At the last follow-up, 17 patients had died from COVID-19 (n = 8) or PD (n = 9) giving an estimated 73% four-month overall survival rate. SARS-CoV-2 infection has a heterogenous course in cancer patients. Lymphocytopenia carries a significant risk of severe/critical COVID-19. SARS-CoV-2 disruption of therapy is as serious as SARS-CoV-2 infection itself. Careful surveillance will allow early restart of the anti-cancer treatment.