Every patient has the right to receive optimal quality health care. With regard to pathology practice, a small (interpretational) difference can have major impact for the patient, because prognosis and treatment selection are often based on the pathology report. Unfortunately, it is inevitable that errors may and do ultimately arise, and it is the task of all involved to minimize the error rate.

In this thesis, we aimed to assess and improve the quality of several important aspects of pathology practice, and thereby improve quality of health care and patient safety. To this end, several diagnostic processes in pathology practice were assessed, and the added value of multiple interventions or strategies, with focus on oncology, was investigated.

First, we addressed the problem of high pathologist workload, which is expected to compromise quality of pathology. Pathologist workload can be decreased by task redistribution by the employment of pathologist’s assistants to take over a selection of routine tasks from pathologists. We assessed whether deployment of pathologist’s assistants, who lack the 5-year training in pathology, would hamper quality of patient care in one specific aspect: harvesting lymph nodes from colorectal cancer resection specimens. We demonstrated that pathologist’s assistants in fact contributed to quality improvement.

The second very common problem we addressed was interobserver variation. The first step towards standardization is providing insight into the presence of this variation. We demonstrated considerable variation between and within Dutch pathology laboratories with regard to the grading of colorectal adenomas and adenocarcinomas, emphasizing that standardization of histological grading is needed, e.g. by education. Other possible interventions to improve standardization are giving feedback on performance (to pathologists, laboratories, and clinicians) and incorporating redundancy in the diagnostic process. Redundancy was incorporated firstly by double reading of a selection of histo- and cytopathology specimens (by specialized pathologists). Double reading resulted in a major discordant diagnosis with potential clinical significance in about 1% and 13% of the histopathology and cytopathology cases, respectively. Secondly, routine co-testing of all invasive breast cancers for HER-2 status by immunohistochemistry and a gene amplification test (e.g. multiplex ligation-dependent probe amplification) revealed a discordance between the two tests in 11/595 (1.8%) of cases and may thereby improve the quality of HER-2 testing.

In addition, we demonstrated that autopsies are still an important quality assessment instrument, even in the era of high-tech medicine, as major discrepancies, related to the cause of death, persist in 23.5% of cases when clinical diagnoses and autopsy findings were compared using the Goldman classification.

Although the interventions will slightly increase costs of pathology, the relative global costs of pathology will still be minute, and we expect that by investing in good quality of pathology practice, costs can be saved elsewhere, e.g. costs of incorrect treatment, unnecessary hospital stay, or possible litigation costs in case of an incorrect diagnosis.

The results of this thesis will hopefully stimulate laboratories/pathologists to incorporate one or more of the quality interventions into their own practice.