When Then Muliple Colum Update 1 Statement

I have about 5 statements like the update below, depending on the PID different columns will be update "C2005, G2005,E2005...."

I would like to use 1 update statement in stead of 5 to update all columns below are 2 original update statements and my attempt at when then update. Note a different column is updated depending on the PID.

If when then isnt possible, any other suggestions are welcomed. Thanks
UPDATE #Sec
SET C2005 = Pos.USD / 1000
FROM #Sec INNER JOIN
Pos ON #Sec.ID = Pos.ID
WHERE (Pos.PID = 'B')

UPDATE #Sec
SET G2005 = Pos.USD / 1000
FROM #Sec INNER JOIN
Pos ON #Sec.ID = Pos.ID
WHERE (Pos.PID = 'G')

UPDATE #Sec
WHEN (Pos.PID = 'C') THEN SET C2005 = Pos.USD / 1000 end
WHEN (Pos.PID = 'G') THEN SET G2005 = Pos.USD / 1000 end
WHEN (Pos.PID = 'E') THEN SET E2005 = Pos.USD / 1000 end
FROM #Sec INNER JOIN
Pos ON #Sec.ID = Pos.ID