The breast is a double glandular organ located on the front side of the chest. It is a mammary gland that consists of 15-25 lobes, of which the main role is producing milk in the lactation period. There are many pathological processes that can occur in breasts and they are mainly benign (inflammatory changes, cysts, fibrocystic changes). Breast tumours can be benign or malignant. The most common benign breast tumors are fibroadenoma and the philloid tumor, and a primary malignant tumor is mostly adenocarcinoma (the most common - ductal invasive carcinoma). The death rate from breast cancer makes up around 20% of the total death rate when it comes to women, and it is a great public health issue in the whole world. With the aim of detecting breast cancer by using a non-invasive method, the FNAB (Fine-needle aspiration biopsy) is a fast, inexpensive and reliable method, and less invasive than core biopsy. Obtaining a sample by cytologic puncture is a standard diagnostic method after which the sample is stained according to May - Gruenwald - Giemsa method (MGG) and analysed under a microscope. Cytological findings are descriptive, and do not always end with a definite diagnosis. The National Cancer Institute (NCI) in collaboration with the World Health Organization (WHO) in 1996 proposed a standardized classification of cytological reports of the breast. The cytological reports are classified into 5 categories. C1 is a category of inadequate samples that are insufficient for analysis. The C2 category is characterized by patterns of benign breast changes. C3 is a category that comprises samples with atypical characteristics, most probably of benign origin. C4 is a category that includes samples where the atypia is more pronounced and is suspicious for malignancy. The C5 category includes undoubtedly malignant patterns. The ratio of certain categories of findings in different cytological laboratories depends on several factors. The goal is to achieve as few inadequate samples as possible. The C3 and C4 categories are often the subject of discussion because the criteria are not always fully defined, but data from literature justifies the existence of these two distinct categories, because within C3 there is about 35% of malignant tumours and in group C4 there is as much as 81-86% of cancers on final PH diagnosis. The implementation of standardized classifications and reporting of various morphological analyses, including cytology, is very important in order to standardize further diagnostic and therapeutic procedures, facilitate understanding and comparison between laboratories and ensure better quality control.