▁T ogether ▁with ▁his ▁son ▁Chris , ▁Cal le ▁returned ▁to ▁the ▁subject ▁of ▁space ▁expl oration ▁with ▁a ▁pair ▁of ▁st amps ▁issued ▁in ▁ 1 9 9 4 ▁in ▁honor ▁of ▁the ▁ 2 5 th ▁anni versary ▁of ▁the ▁Apol lo ▁ 1 1 ▁mission ▁and ▁the ▁first ▁man ned ▁moon ▁landing . ▁ ▁Works ▁ ▁Cal le ▁produced ▁do z ens ▁of ▁post age ▁stamp ▁designs , ▁featuring ▁such ▁individuals ▁as ▁Douglas ▁Mac Ar thur ▁and ▁Robert ▁F rost . ▁He ▁also ▁produced ▁Western - th emed ▁art works ▁that ▁have ▁been ▁shown ▁at ▁the ▁National ▁Cow boy ▁& ▁Western ▁Heritage ▁Museum , ▁as ▁well ▁as ▁a ▁ 1 9 8 1 ▁stamp ▁hon oring ▁Freder ic ▁Rem ington . ▁His ▁dep ict ions ▁of ▁the ▁American ▁West ▁have ▁been ▁included ▁in ▁the ▁collections ▁of ▁the ▁Gil cre ase ▁Museum ▁in ▁Tul sa , ▁Oklahoma ▁and ▁at ▁the ▁Bo oth ▁Western ▁Art ▁Museum ▁in ▁Car ters ville , ▁Georgia . ▁ ▁Health , ▁later ▁life , ▁and ▁death ▁ ▁After ▁do ctors ▁discovered ▁that ▁his ▁mel an oma ▁had ▁met ast as ized , ▁he ▁was ▁placed ▁on ▁int ra ven ous ▁I p il imum ab , ▁an ▁experimental ▁treatment ▁being ▁tested ▁by ▁Br istol - My ers ▁S qu ib b ▁that ▁is ▁meant ▁to ▁improve ▁the ▁response ▁by ▁the ▁imm une ▁system ▁to ▁fight ▁cancer . ▁An ▁initial ▁course ▁of ▁treatment ▁with ▁the ▁test ▁drug ▁combined ▁with ▁chem other apy ▁left ▁no ▁trace ▁of ▁the ▁cancer