A pharmaceutical composition comprising BIBW 2992 or a pharmaceutically acceptable salt thereof, for use in a method for treatment of a non-small cell lung cancer (NSCLC) patient by a method comprising (a) identifying a patient in need of treatment with BIBW 2992 or a pharmaceutically acceptable salt thereof; (b) determining that the patient is receiving therapy with a P-gp inhibitor selected from alfentanil, amiloride, amiodarone, amitriptyline, astemizole, atovaquone, atorvastatin, azelastine, azidopine, azithromycin, bepridil, biricodar, bromocriptine, carbamazepine, carvedilol, chloroquine, chlorpromazine, clarithromycin, cyclosporin, cyproheptadine, darunavir, desethylamiodarone, desipramine, dexniguldipine, dexrazoxane, diltiazem, dipyridamole, disulfiram, doxazosin, elacridar, emetine, erythromycin, felodipine, fenofibrate, fentanyl, flavonoids, fluoxetine, fluphenazine, fluvoxamine, fucidin, gallopamil, glyburide, gramicidin D, grapefruit juice, garlic, green tea, haloperidol, hydrocortisone, hyroxyzine, josamycin, ketoconazole, imipramine, itraconazole, ivermectin, ketoconazole, laniquidar, lansoprazole, levothyroxin, lidocaine, loperamide, lopinavir, loratadine, lovastatin, maprotiline, mefloquine, methadone, mibefradil, midazolam, mitomycin C, nefazodone, nelfinavir, nicardipine, nitrendipine, nobiletin, norverapamil, omeprazole, orange juice, ofloxacin, paroxetine, pantoprazole, phenothiazines, phenobarbital, piperine, pimozide, probenecid, progesterone, promethazine, propafenone, propranolol, quercetin, quinacrine, quinidine, quinine, reserpine, ritonavir, saquinavir, sertraline, simvastatin, spironolactone, sufentanil, tacrolimus, tamoxifen, tariquidar, telithromycin, terfenadine, testosterone, tetrabenazine, thioridazine, trifluoperazine, trifluopromazine, trimipramine, valinomycin, vanadate, venlafaxine, verapamil, vinblastine, FK506, RU486(mifepristone), valspodar PSC 833, zosuquidar and 2n-propylquinoline or combinations thereof; (c) causing the patient's therapy with the P-gp inhibitor to cease prior to treatment with BIBW 2992 or a pharmaceutically acceptable salt thereof; (d) administering BIBW 2992 or a pharmaceutically acceptable salt thereof to the patient; (e) resuming therapy with a P-gp inhibitor not earlier than 6 hours after the administration of BIBW 2992 or a pharmaceutically acceptable salt thereof (a) identifying a patient in need of treatment with BIBW 2992 or a pharmaceutically acceptable salt thereof; (b) determining that the patient is receiving therapy with a P-gp inhibitor selected from alfentanil, amiloride, amiodarone, amitriptyline, astemizole, atovaquone, atorvastatin, azelastine, azidopine, azithromycin, bepridil, biricodar, bromocriptine, carbamazepine, carvedilol, chloroquine, chlorpromazine, clarithromycin, cyclosporin, cyproheptadine, darunavir, desethylamiodarone, desipramine, dexniguldipine, dexrazoxane, diltiazem, dipyridamole, disulfiram, doxazosin, elacridar, emetine, erythromycin, felodipine, fenofibrate, fentanyl, flavonoids, fluoxetine, fluphenazine, fluvoxamine, fucidin, gallopamil, glyburide, gramicidin D, grapefruit juice, garlic, green tea, haloperidol, hydrocortisone, hyroxyzine, josamycin, ketoconazole, imipramine, itraconazole, ivermectin, ketoconazole, laniquidar, lansoprazole, levothyroxin, lidocaine, loperamide, lopinavir, loratadine, lovastatin, maprotiline, mefloquine, methadone, mibefradil, midazolam, mitomycin C, nefazodone, nelfinavir, nicardipine, nitrendipine, nobiletin, norverapamil, omeprazole, orange juice, ofloxacin, paroxetine, pantoprazole, phenothiazines, phenobarbital, piperine, pimozide, probenecid, progesterone, promethazine, propafenone, propranolol, quercetin, quinacrine, quinidine, quinine, reserpine, ritonavir, saquinavir, sertraline, simvastatin, spironolactone, sufentanil, tacrolimus, tamoxifen, tariquidar, telithromycin, terfenadine, testosterone, tetrabenazine, thioridazine, trifluoperazine, trifluopromazine, trimipramine, valinomycin, vanadate, venlafaxine, verapamil, vinblastine, FK506, RU486(mifepristone), valspodar PSC 833, zosuquidar and 2n-propylquinoline or combinations thereof; (c) causing the patient's therapy with the P-gp inhibitor to cease prior to treatment with BIBW 2992 or a pharmaceutically acceptable salt thereof; (d) administering BIBW 2992 or a pharmaceutically acceptable salt thereof to the patient; (e) resuming therapy with a P-gp inhibitor not earlier than 6 hours after the administration of BIBW 2992 or a pharmaceutically acceptable salt thereof