The present inventors show that cannibal cells can undergo senescence after entosis in vivo and that the tumor suppressive protein p53 act as a repressor of this phenomenon. They therefore propose new tools to study the molecular pathways involved in the cannibalism process, for example by measuring the expression levels of p53 or splice variants thereof (such as Δ133TP53, TP53β, TP53γ or Δ40TP53), the release of extracellular ATP or purinergic P2Y2 receptor activity. The present inventors also demonstrated that the detection of senescent cannibal cells in breast adenocarcinoma obtained from patients treated with neo-adjuvant therapy positively correlates with good patient's response to treatment. Altogether, these results provide the first evidence that detection of cellular cannibalism and senescence simultaneously in tumors helps for the diagnosis of disease outcomes and for the prediction of treatment efficiency against cancer diseases.