Study the relationship between the given pair of letter clusters and identify the pattern of transformation. Use the same rule to find the missing letter cluster.
$$\text{ILGDC}:\text{KNIFE}::\text{DPMLB}:\_\_\_\_\_::\text{QUMPB}:\text{SWORD}$$

Let's examine the shift between corresponding letters in the established sets:
Set 1: $\text{ILGDC}\to \text{KNIFE}$

* $I\stackrel{+2}{\to }K$
* $L\stackrel{+2}{\to }N$
* $G\stackrel{+2}{\to }I$
* $D\stackrel{+2}{\to }F$
* $C\stackrel{+2}{\to }E$

Set 3: $\text{QUMPB}\to \text{SWORD}$

* $Q\stackrel{+2}{\to }S$
* $U\stackrel{+2}{\to }W$
* $M\stackrel{+2}{\to }O$
* $P\stackrel{+2}{\to }R$
* $B\stackrel{+2}{\to }D$

The constant pattern is a $+2$ shift forward in alphabetical positions. Applying this to $\text{DPMLB}$:

* $D\stackrel{+2}{\to }F$
* $P\stackrel{+2}{\to }R$
* $M\stackrel{+2}{\to }O$
* $L\stackrel{+2}{\to }N$
* $B\stackrel{+2}{\to }D$

The missing letter cluster is FROND.