Triple-negative breast cancer (TNBC) is a highly malignant tumor histotype which lacks effective targeted therapies, thereby being considered as the most aggressive form of breast carcinoma. To identify novel compounds which could counteract TNBC cell growth, we explored the in vitro effects of crude extracts and <10 kDa-filtered fractions of the coelomic fluid obtained from the sea urchin Arbacia lixula on TNBC MDA-MB231 cells. We examined cell viability, cycle distribution, apoptotic/autophagic activity, and mitochondrial polarization/cell redox status. Here, we report the first data demonstrating an anti-TNBC effect by A. lixula-derived coelomic fluid extracts. Thus, identification of the water-soluble bioactive component(s) contained in the extracts deserve(s) further investigation aimed to devise novel promising prevention and/or treatment agents effective against highly malignant breast tumors.Further studies conducted by Björn et al. [8] demonstrated that the synthetic peptides sequentially derived from the previously characterized centrocin 1 (CEN1 HC-Br and CEN1 HC) showed prominent microbicidal and anti-inflammatory activities on in vivo and in vitro mammalian models, representing an interesting resource for the treatment of infections in humans.Furthermore, a recent study by Katelnikova et al. [9] highlighted that a glycopeptide fraction (GPF) derived from internal organs of the green sea urchins Strongylocentrotus droebachiensis possesses relevant anti-inflammatory effects, especially for the treatment of bronchitis. Moreover, the absorption and pharmacokinetics of GPF following single and repeated intranasal administration were evaluated over the course of seven days in rats [10].Another echinoderm species from which bioactive molecules were studied is Arbacia lixula, commonly found in the Mediterranean Sea and in the African Atlantic coast [11]. So far, the biomedical applications of molecules extracted from this marine invertebrate are very limited. Of note, Stabili et al. [12] demonstrated the powerful antioxidant effect exerted by the lysate of A. lixula's coelomocytes, the immune cells present in the coelomic fluid (CF) of the sea urchin, whereas Cirino et al. [13] highlighted that A. lixula's eggs are a rich source of astaxanthin, a radical scavenger that can prevent neurodegenerative diseases. These promising findings prompted an extension of the study on the pharmacological potential of A. lixula-derived substances, whose massive sourcing represents an easy task due to the abundance of this marine species in waters surrounding Sicily, also being a thermophilic species which is expanding very quickly due to the increase of the surface temperature of the Mediterranean Sea [14].Triple-negative breast cancers (TNBC) are categorized among the highly "aggressive" malignant carcinomas. In fact, the lack of expression of estrogen, progesterone, and epidermal growth factor type 2 (HER2) receptors makes them poorly responsive to hormonal therapies and to HER2-targeting drugs, and the TNBC histotype ...