  In the Milky Way there are thousands of stellar clusters each harboring from
a hundred to a million stars. Although clusters are common, the initial
conditions of cluster formation are still not well understood. To determine the
processes involved in the formation and evolution of clusters it is key to
determine the global properties of cluster-forming clumps in their earliest
stages of evolution. Here, we present the physical properties of 1,244 clumps
identified from the MALT90 survey. Using the dust temperature of the clumps as
a proxy for evolution we determined how the clump properties change at
different evolutionary stages. We find that less-evolved clumps exhibiting dust
temperatures lower than 20 K have higher densities and are more gravitationally
bound than more-evolved clumps with higher dust temperatures. We also
identified a sample of clumps in a very early stage of evolution, thus
potential candidates for high-mass star-forming clumps. Only one clump in our
sample has physical properties consistent with a young massive cluster
progenitor, reinforcing the fact that massive proto-clusters are very rare in
the Galaxy.
