The expression of the human Ki-67 protein is strictly associated with cell proliferation. During interphase, the antigen can be exclusively detected within the nucleus, whereas in mitosis most of the protein is relocated to the surface of the chromosomes. The fact that the Ki-67 protein is present during all active phases of the cell cycle (G(1), S, G(2), and mitosis), but is absent from resting cells (G(0)), makes it an excellent marker for determining the so-called growth fraction of a given cell population. In the first part of this study, the term proliferation marker is discussed and examples of the applications of anti-Ki-67 protein antibodies in diagnostics of human tumors are given. The fraction of Ki-67-positive tumor cells (the Ki-67 labeling index) is often correlated with the clinical course of the disease. The best-studied examples in this context are carcinomas of the prostate and the breast. For these types of tumors, the prognostic value for survival and tumor recurrence has repeatedly been proven in uni- and multivariate analysis. The preparation of new monoclonal antibodies that react with the Ki-67 equivalent protein from rodents now extends the use of the Ki-67 protein as a proliferation marker to laboratory animals that are routinely used in basic research. The second part of this review focuses on the biology of the Ki-67 protein. Our current knowledge of the Ki-67 gene and protein structure, mRNA splicing, expression, and cellular localization during the cell-division cycle is summarized and discussed. Although the Ki-67 protein is well characterized on the molecular level and extensively used as a proliferation marker, the functional significance still remains unclear. There are indications, however, that Ki-67 protein expression is an absolute requirement for progression through the cell-division cycle.

The Ki‐67 protein: From the known and the unknown

Tumours grow within an intricate network of epithelial cells, vascular and lymphatic vessels, cytokines and chemokines, and infiltrating immune cells. Different types of infiltrating immune cells have different effects on tumour progression, which can vary according to cancer type. In this Opinion article we discuss how the context-specific nature of infiltrating immune cells can affect the prognosis of patients.

The immune contexture in human tumours: impact on clinical outcome

One of the main engines that drives cellular transformation is the loss of proper control of the mammalian cell cycle. The cyclin-dependent kinase inhibitor p21 (also known as p21WAF1/Cip1) promotes cell cycle arrest in response to many stimuli. It is well positioned to function as both a sensor and an effector of multiple anti-proliferative signals. This Review focuses on recent advances in our understanding of the regulation of p21 and its biological functions with emphasis on its p53-independent tumour suppressor activities and paradoxical tumour-promoting activities, and their implications in cancer.

p21 in cancer: intricate networks and multiple activities

Hyaluronan is an extracellular and cell-surface-associated polysaccharide that is traditionally regarded as a biological 'goo' that participates in lubricating joints or holding together gel-like connective tissues. Although these are common physiological roles of hyaluronan in adult organisms, hyaluronan also functions as a microenvironmental cue that co-regulates cell behaviour during embryonic development, healing processes, inflammation and tumour development. Recent work highlights a key role for interactions between hyaluronan and tumour cells in several aspects of malignancy and indicates the possibility of new therapeutic strategies.

Hyaluronan: from extracellular glue to pericellular cue

EAU Guidelines on Non-Muscle-invasive Urothelial Carcinoma of the Bladder: Update 2016.

Lymphocyte infiltrates as a prognostic variable in female breast cancer

Apoptosis in breast cancer as related to histopathological characteristics and prognosis

High stromal hyaluronan level is associated with poor differentiation and metastasis in prostate cancer

The expression of bcl-2 protein was analysed immunohistochemically in 202 female breast carcinomas. The intensity of bcl-2 expression was inversely related to tumour grade (P < 0.0001), tumor necrosis (P < 0.0001), mitotic index (P < 0.0001), oestrogen receptor content (P < 0.0001), progesterone receptor content (P = 0.0007), S-phase fraction (P = 0.00047), and apoptotic index (P = 0.087). A high fraction of bcl-2-positive cells was related to ductal or lobular type (P = 0.03) and slight nuclear pleomorphism (P = 0.03). Heterogeneous expression of bcl-2 protein was associated with high grade (P = 0.02), severe nuclear pleomorphism (P = 0.02), DNA aneuploidy (P = 0.018), high S-phase fraction (P = 0.05), and early metastasis (P = 0.03). Intense expression of bcl-2 protein was significantly related to favourable outcome in the entire cohort (P = 0.0013), as well as in axillary lymph node-negative (ANN) tumours (P = 0.0124). Long recurrence-free periods in the entire cohort (P = 0.037) and in ANN tumours (P = 0.08) were confined to cases with intense expression of bcl-2 protein. In multivariate analysis, bcl-2 expression had no independent prognostic value in the entire cohort or in axillary lymph node-negative breast carcinomas, whereas it was a weak independent prognostic factor in axillary lymph node-positive breast carcinomas.

Apoptosis suppressing protein bcl-2 is expressed in well-differentiated breast carcinomas with favourable prognosis.

Four hundred cases of transitional cell bladder cancer were reviewed by light microscopy for the presence of apoptotic cells in the primary tumour biopsy specimens. The number of apoptotic cells/mm2 of neoplastic epithelium (apoptotic index, AI) was related to various histological features and prognosis. AI was related significantly to high T-category, high grade, DNA aneuploidy, large nuclear morphometric variable values, and high proliferation rate of cancer cells. Tumours showing overexpression of p53 oncoprotein in over 10 per cent of the nuclei had significantly higher AI values than p53-negative tumours. Multivariate regression analysis showed that AI was independently predicted by mitotic index, mean nuclear area, and papillary status. Progression, recurrence-free survival, and survival of superficial tumours were all related significantly to AI. In multivariate survival analysis, T-category, papillary status, grade, and mitotic index had independent prognostic value, while the recurrence-free survival of Ta-T1 tumours was related independently to AI. The results show that AI is related particularly to mitotic activity in transitional cell bladder tumours, while AI as assessed by light microscopy hardly has any independent prognostic significance.

Sirpa Aaltomaa

Papers

Lymphocyte infiltrates as a prognostic variable in female breast cancer

Apoptosis in breast cancer as related to histopathological characteristics and prognosis

High stromal hyaluronan level is associated with poor differentiation and metastasis in prostate cancer

Apoptosis suppressing protein bcl-2 is expressed in well-differentiated breast carcinomas with favourable prognosis.

Apoptosis in bladder cancer as related to standard prognostic factors and prognosis.