Inhibition of Janus-kinase 1/2 (JAK1/2) is a mainstay to treat myeloproliferative neoplasms (MPN). Sporadic observations reported the co-incidence of B-cell non-Hodgkin lymphomas during treatment of MPN with JAK1/2 inhibitors. We assessed 626 patients with MPN, including 69 with myelofibrosis receiving JAK1/2 inhibitors for lymphoma development. B-cell lymphomas evolved in 4 (5.8%) of 69 patients receiving JAK1/2 inhibition compared with 2 (0.36%) of 557 with conventional treatment (16-fold increased risk). A similar 15-fold increase was observed in an independent cohort of 929 patients with MPN. Considering primary myelofibrosis only (N = 216), 3 lymphomas were observed in 31 inhibitor-treated patients (9.7%) vs 1 (0.54%) of 185 control patients. Lymphomas were of aggressive B-cell type, extranodal, or leukemic with high MYC expression in the absence of V617F or other MPN-associated mutations. Median time from initiation of inhibitor therapy to lymphoma diagnosis was 25 months. Clonal immunoglobulin gene rearrangements were already detected in the bone marrow during myelofibrosis in 16.3% of patients. Lymphomas occurring during JAK1/2 inhibitor treatment were preceded by a preexisting B-cell clone in all 3 patients tested. Sequencing verified clonal identity in 2 patients. The effects of JAK1/2 inhibition were mirrored in mice: 16 of 24 mice developed a spontaneous myeloid hyperplasia with the concomitant presence of aberrant B cells. Transplantations of bone marrow from diseased mice unmasked the outgrowth of a malignant B-cell clone evolving into aggressive B-cell leukemia-lymphoma. We conclude that JAK/STAT1 pathway inhibition in myelofibrosis is associated with an elevated frequency of aggressive B-cell lymphomas. Detection of a preexisting B-cell clone may identify individuals at risk.

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Therapy of canine mammary tumours (CMTs) with classical antitumour drugs is problematic, so better therapeutic options are needed. Palbociclib (PD-0332991) is an innovative and effective anticancer drug for the treatment of breast cancer in women. Palbociclib is an inhibitor of cyclin-dependent kinase 4 (CDK4) and CDK6, which are key regulators of the cell cycle machinery and thus cell proliferation. In the present in vitro study, we investigated whether Palbociclib also represents a candidate drug to combat CMT. For this purpose, the effect of Palbociclib was analysed in P114 and CF41 cells, two CMT cell lines with an endogenous CDK4/6 co-expression. Incubation of P114 and CF41 cells with Palbociclib resulted in a dose-and timedependent loss of phosphorylated retinoblastoma protein (pRb), a classical CDK4/6 substrate within the cell cycle machinery. Moreover, treatment of CMT cells with Palbociclib-induced cell cycle arrest affected cell viability, prevented colony formation and impaired cell migration activity. Palbociclib also inhibited the growth of P114 and CF41 cell spheroids. Immunohistochemical analysis of canine patient samples revealed a consistent expression of CDK6 in different canine mammary carcinoma types, but an individual and tumour-specific expression pattern of phosphorylated pRb independent of the tumour grade. Together, our findings let us suggest that Palbociclib has antitumour effects on CMT cells and that canine patients may represent potential candidates for treatment with this CDK4/6 inhibitor. K E Y W O R D S canine mammary tumour, CDK4/6, cell cycle, migration, Palbociclib

The opioid crisis of pain medication bears risks from addiction to cancer progression, but little experimental facts exist. Expression of δ-opioid receptors (DORs) correlates with poor prognosis for breast cancer (BCa) patients, but mechanism and genetic/pharmacologic proof of key changes in opioid-triggered cancer biology are lacking. We show that oncogenic STAT3 signaling and E-Cadherin downregulation are triggered by opioid-ligated DORs, promoting metastasis. Human and murine transplanted BCa cells (MDA-MB-231, 4T1) displayed enhanced metastasis upon opioid-induced DOR stimulation, and DOR-antagonist blocked metastasis. Opioid-exposed BCa cells showed enhanced migration, STAT3 activation, down-regulation of E-Cadherin and expression of epithelial-mesenchymal transition (EMT) markers. STAT3 knockdown or upstream inhibition through the JAK1/2 kinase inhibitor ruxolitinib prevented opioid-induced BCa cell metastasis and migration. We conclude that opioids trigger metastasis through oncogenic JAK1/2-STAT3 signaling.