Cubical Acyclic Homotopy Excision
  Given a strong homotopy pushout cube of spaces A, we measure how far it is from also being a homotopy pullback cube. Explicitly, letting P be the homotopy colimit of the diagram obtained from A by forgetting the initial vertex $A_\varnothing$, we study the homotopy fibre of the double suspension of the comparison map $A_\varnothing \to P$. This difference is expressible in terms of the homotopy fibres of the original maps in A. 
Kay Werndli
math.AT