Individualization and optimization of risk-adapted therapy in breast cancer requires molecular profiling of individual cancer specimens. In tissues of heterogeneous cellular composition, such as mammary tissue, cancer prognostic markers and potential therapeutic target molecules are preferentially detected by in situ techniques such as immunohistochemistry. The more therapy decisions are based on immunohistochemical findings, the more histopathologists are confronted with the demand to establish standardized procedures that enable reproducible evaluation independent from the investigating laboratory. Disappointing results of recent national and international immunohistochemistry trials for steroid receptor and HER-2 analysis in breast cancer underline the need to act now beyond recommendations and well-formulated guidelines for standardization. In order to ensure staining quality in every individual immunohistochemical analysis, we have developed an on-slide control with standardized samples which are placed on every slide of a therapy-decisive stain together with the tissue of interest. Novel mini tissue microarrays were constructed comprising cell lines as standardized controls, indicating the sensitivity and reliability of the staining procedure. Standardized control material on the same slide as the patient's specimen require neither additional reagents nor time and are automatically archived on the diagnostic slide to prove the quality of staining even after years.