| SAB | Spinal anesthesia; Spinal block; Subarachnoid block |
| SABR | Stereotactic ablative body radiation therapy; Stereotactic body radiation therapy |
| SAHA | Suberoylanilide hydroxamic acid; Vorinostat; Zolinza |
| SAMe disulfate p-toluene-sulfonate | S-adenosyl-L-methionine disulfate p-toluene-sulfonate |
| sarCNU | Sarcosinamide nitrosourea |
| SARS-CoV-2 | Severe acute respiratory syndrome coronavirus 2 |
| SB AS02B | SB-AS02B adjuvant |
| SB-715992 | Ispinesib |
| SBI | Serum-derived bovine immunoglobulin protein isolate |
| SBRT | Stereotactic ablative body radiation therapy; Stereotactic body radiation therapy |
| SC-58635 | Celecoxib |
| SC-70935 | Leridistim |
| SCF | Kit ligand; Stem cell factor |
| SCFA HQK-1004 | Arginine butyrate; Short chain fatty acid HQK-1004 |
| SCH-58500 | rAd/p53; Recombinant adenovirus-p53 |
| SCID | Severe combined immunodeficiency disease |
| SCIG | Immune globulin subcutaneous human-klhw |
| SC-PEG rADA | Elapegademase |
| SDOH | Social determinants of health |
| SDR | Second-degree relative |
| SDS | Shwachman syndrome; Shwachman-Diamond syndrome |
| SDX-102 | Alanosine |
| Se | Selenium |
| SEB | Staphylococcal enterotoxin B |
| SEGA | Subependymal giant cell astrocytoma |
| SeMet | L-selenomethionine |
| sEphB4-HSA | Recombinant EphB4-HSA fusion protein |
| SERD | Selective estrogen receptor degrader |
| SERM | Selective estrogen receptor modulator |
| SES | Socioeconomic status |
| SF6 | Sulfur hexafluoride |
| SFI | Shenqi Fuzheng injection SQ001 |
| SG | Sodium glycididazole |
| SGI-110 | Guadecitabine |
| SGN-35 | Adcetris; Brentuximab vedotin |
| SGOT | Aspartate transaminase; Serum glutamic-oxaloacetic transaminase |
| SGPT | Alanine transferase; Serum glutamate pyruvate transaminase |
| SHM | Spiromustine |
| SHS | Synthetic human secretin |
| SIDS | Crib death; Sudden infant death syndrome |
| SIL | Squamous intraepithelial lesion |
| SIRS | Systemic inflammatory response syndrome |
| SJDBT | Sipjeondaebo-tang |
| SK2 inhibitor ABC294640 | Opaganib |
| SK&F106615 | Atiprimod; Azaspirane |
| SLE | Systemic lupus erythematosus |
| SLI381 | Dextroamphetamine-amphetamine |
| SLL | Small lymphocytic lymphoma; Well-differentiated lymphocytic lymphoma |
| SLM | Sirolimus |
| SM-AHN | Systemic mastocytosis with associated hematologic neoplasm |
| SMD | Simo decoction |
| SMZ-TMP | Trimethoprim-sulfamethoxazole |
| Sn-117m DTPA | Tin Sn 117m DTPA |
| SNDX-275 | Entinostat; HDAC inhibitor SNDX-275 |
| SnET2 | Rostaporfin; Tin ethyl etiopurpurin |
| SNP | Single nucleotide polymorphism |
| SNRI | Serotonin-norepinephrine reuptake inhibitor |
| SNV | Single nucleotide variant |
| SOM230 LAR | Long-acting release pasireotide |
| SOP | Standard Operating Procedure |
| SPECT | Single-photon emission computed tomography |
| SPF | Sun protection factor |
| SPG | Spirogermanium |
| SPL | Spironolactone |
| SPP | Sodium pentaborate pentahydrate |
| SP-PG | Tecogalan sodium |
| SP-SAP | Substance P-saporin |
| SQZ-AAC-HPV | Squeezed red blood cells expressing HPV16 epitopes SQZ-AAC-HPV |
| Sr89 | Strontium chloride Sr 89 |
| SRS | Octreotide scan; Somatostatin receptor scintigraphy |
| SRV | Survivin antigen |
| SRV PEP VAC | HLA-A1, A2, B35-restricted survivin peptides/Montanide ISA-51 vaccine |
| SS1(dsFv) PE38 | SS1(dsFv)-PE38 immunotoxin |
| SSG | Sodium stibogluconate |
| SSRI | Selective serotonin reuptake inhibitor |
| ST1481 | Gimatecan |
| STAT3 decoy ODN | STAT3 decoy oligonucleotide |
| STD | Sexually transmitted disease; Sexually transmitted infection |
| STI | Sexually transmitted disease; Sexually transmitted infection |
| STI571 | Gleevec; Imatinib mesylate; Imkeldi |
| STN | Streptonigrin |
| STS | Sodium thiosulfate |
| STS inhibitor BN 83495 | Steroid sulfatase inhibitor BN 83495 |
| STZ | Streptozocin |
| SU006668 | Orantinib |
| SU011248 | Sunitinib malate; Sutent |
| SU101 | Leflunomide |
| SU11248 | Sunitinib malate; Sutent |
| SU5416 | Semaxanib |
| SU6668 | Orantinib |
| SULIN | Sulindac |
| SV40 | Simian virus 40 |
| SVP-R | Synthetic vaccine particles-rapamycin |
| SVV-001 | Seneca Valley virus-001 |
| SWS | Sturge-Weber syndrome |
| SZKJT | San zhong kui jian tang |