Tumors are not merely masses of neoplastic cells but complex tissues composed of cellular and noncellular elements. This review provides recent data on the main components of a dynamic system, such as carcinoma associated fibroblasts that change the extracellular matrix (ECM) topology, induce stemness and promote metastasis-initiating cells. Altered production and characteristics of collagen, hyaluronan and other ECM proteins induce increased matrix stiffness. Stiffness along with tumor growth-induced solid stress and increased interstitial fluid pressure contribute to tumor progression and therapy resistance. Second, the role of immune cells, cytokines and chemokines is outlined. We discuss other noncellular characteristics of the tumor microenvironment such as hypoxia and extracellular pH in relation to neoangiogenesis. Overall, full understanding of the events driving the interactions between tumor cells and their environment is of crucial importance in overcoming treatment resistance and improving patient outcome.

Background: Breast cancer treatment trends are currently based on tailored therapies using tumor and patient biomarkers. Lapatinib is the first dual inhibitor of HER1 (EGFR, ErbB1) and HER2 (ErbB2, Neu) tyrosine kinases to be used in clinical ...

Aims and Background: Lapatinib is a tyrosine kinase inhibitor targeting epidermal growth factor receptors 1 (EGFR/HER1) and 2 (HER2) used in the treatment of patients with HER2-positive breast cancer. The aim of the present study was to determine lapatinib plasma levels in breast cancer patients treated with lapatinib plus capecitabine. Patients and Methods: We assessed lapatinib plasma levels in blood samples from 21 breast cancer patients treated with lapatinib plus capecitabine using the standard regimen in an expanded access program. Liquid chromatography tandem mass spectrometry was used for measuring lapatinib plasma concentrations. The validated method was applied for measurement of 55 plasma samples. Results: The median lapatinib plasma level was 5.09 μg/mL, with large interindividual differences. Patients of lower weight tended to have higher lapatinib plasma levels (Spearman correlation coefficient R = −0.435, P = 0.055). One patient's lapatinib plasma levels were markedly higher than those of the others, with a median level of 11.25 μg/mL and repeatedly exceeding 7.80 μg/mL. The treatment was terminated after 8 months when hyperbilirubinemia occurred. Conclusions: The lapatinib plasma levels reported here are twice as high as the clinically effective steady-state geometric mean maximum concentration. We conclude that increased lapatinib body levels occur when patients are in a nonfasting state at the time of drug intake and when lapatinib doses are not adjusted to low body weight or weight loss during treatment. In Europe, dose adjustments are not recommended in the case of hepatic function impairment. Thus, attention should be paid to changes in liver function test results in clinical practice, especially in patients of small stature and weight, given the risk of high plasma concentrations. Prospective lapatinib plasma level assessment in treated patients might be useful to confirm or refute the possible correlation of high lapatinib plasma levels with hepatic and/or other toxicities.