Tumor regression and relapse on prolonged

MYC inactivation. (A) Transplantation of tumor cells into a syngeneic recipient results in the animal becoming moribund with tumor burden, as demonstrated grossly by tumor invasion into thymus, lymph nodes, spleen, liver, and intestine and histologically by the effacement of spleen architecture. (B) AfterMYC inactivation with doxycycline treatment for 2 weeks, autopsy and histologic examination show evidence of complete tumor regression and the restoration of healthy spleen architecture. (C) After prolonged MYC inactivation, tumors can relapse, again invading the thymus, spleen, lymph nodes, liver, and intestine. Histologic specimens were stained with hematoxylin and eosin. Bottom panels show × 10 and × 60 (inset) images of the spleen. LN indicates lymph node; SC, superficial cervical; P, popliteal; M, mesenteric.