Although COVID-19 has had dire consequences on diagnosis of cancer, little data assessing its impact on the whole range of diagnostic activity relevant to cancer are available. We examined trends in the provision of full diagnostic tests for consecutive patients with suspected cancer referred to an academic hospital-based Quick Diagnosis Unit from January 2019 to December 2020. As weekly volumes declined, waiting times for endoscopic, imaging and biopsy/cytology procedures increased steeply during the COVID-impacted period (26 February–28 April 2020). The average weekly increase compared with the same period in 2019 was substantial for invasive procedures requiring admission (200.70%), CT scans (171.20%), GI endoscopy (161.50%), PET/CT scans (152.50%), ultrasonography (148.40%), and ambulatory biopsy/cytology procedures (111.20%). Volumes and waiting times to other procedures showed similar trends. There was a remarkable downward trend in cancer diagnosis during the COVID-impacted period, with a 54.07% reduction compared with the same weeks in 2019. Despite a modest recovery in the following months, the decline in weekly activity and cancer rates persisted until 30 December. Providing insight into how COVID-19 changed the full spectrum of diagnostic activity for suspected cancer informs resilience-building interventions to guarantee access to fast and efficient diagnostics ahead of new threats.