Viral Claim About “Single Dose” Cancer Drug Causing Tumor to Vanish in 5 Days Is Misleading

A recent social-media claim is circulating widely, stating that a “single dose” of a new experimental cancer drug caused a woman’s tumor to “nearly vanish” within just five days. Upon our investigation, we found the claim is misleading.

Social Media Posts

The viral posts claim that “a single dose of a new experimental cancer drug caused a woman’s tumor to shrink dramatically within just 5 days, nearly vanishing from scans.” These posts often lack a specific drug name, trial identifier, or peer-reviewed source.

Source | Archive

Source | Archive

Fact Check

What the Evidence Actually Shows:

Dostarlimab in mismatch repair–deficient rectal cancer

One of the most striking recent cancer breakthroughs involved a drug called dostarlimab (brand name Jemperli) used in a specific type of rectal cancer. The study, conducted at Memorial Sloan Kettering Cancer Center, focused on patients whose tumors had a particular genetic feature called mismatch repair deficiency (dMMR), a characteristic found in only about 5-10% of rectal cancers.

In this small phase 2 trial, all 12 patients received dostarlimab infusions every three weeks for six months. By the end of treatment, every single patient achieved what doctors call a clinical complete response: their tumors could no longer be detected on scans or biopsies, and they didn’t need the surgery or radiation that would normally follow. (Source)

Crucially, this remarkable outcome required multiple doses over half a year, not a single injection, and the tumor disappearance happened gradually over months, not within days. The results apply only to this rare, genetically defined subset of rectal cancer, not to all cancers or even all rectal cancers.

Amivantamab in head & neck / solid tumors

Another important advance involves a drug called amivantamab, which is a bispecific antibody, meaning it targets two different pathways in cancer cells at once (EGFR and MET). This dual-target approach can be particularly effective for certain tumors.

In a recent phase 1b/2 study, researchers tested amivantamab in patients with recurrent or metastatic head and neck squamous cell carcinoma—a type of cancer that had already progressed despite treatment with checkpoint inhibitors (a type of immunotherapy) and platinum-based chemotherapy. These were patients with few remaining treatment options.

The results showed that 45% of patients responded to amivantamab alone, with a median time to first response of about 6.4 weeks (ranging from roughly 5.7 to 18.3 weeks). Additionally, 82% of participants experienced some degree of tumor shrinkage in their target lesions. (Source)

While these results are encouraging and represent meaningful progress for a difficult-to-treat cancer, they still fall well short of the viral claim of “single dose, five-day disappearance.” Responses took weeks to manifest, required multiple doses, and occurred in a specific cancer type with particular molecular characteristics.

Where the Viral Claim Diverges From the Evidence

The evidence shows promising and targeted responses in carefully selected patients, but the viral claim oversimplifies the reality in several important ways:

Dosing schedule: The claim suggests a single injection caused the tumor to disappear. In reality, the dostarlimab trial required injections every three weeks for six months, and the amivantamab trial also involved multiple doses over time.

Speed of response: The viral post claims tumors vanished within five days. The actual data shows responses took much longer: approximately 6-7 weeks for amivantamab patients, and several months for dostarlimab patients.

Applicability: The viral narrative suggests this approach could work for many aggressive cancers. However, these studies targeted very specific cancer subtypes with particular genetic characteristics (dMMR rectal cancer and EGFR/MET-driven tumors) in small, early-phase trials.

Safety profile: The claim implies only cancerous tissue is affected while healthy tissue remains untouched. While these immunotherapies are more targeted than traditional chemotherapy, they can still cause side effects and don’t perfectly distinguish between healthy and malignant cells in all cases.

Level of certainty: The claim presents these results as a proven cure and major breakthrough. In reality, researchers emphasize that these are early findings that require longer follow-up periods, larger patient groups, and testing in diverse populations before drawing definitive conclusions. (Source)

Broader Context and Caution

The remarkable early results in dMMR tumors and the advances in bispecific antibodies illustrate the enormous momentum in cancer research. They do justify cautious optimism, yet medical history reminds us many early-stage successes do not always translate into broadly effective one-shot cures in humans. As editorial commentary in the NEJM noted, the rectal-cancer immunotherapy results are “unheard of” but still require longer follow-up and larger studies. (Source)

Thus, even though the viral claim reflects a desire to simplify and communicate hope, it compresses and merges distinct research findings, overstates the timeline and dosage, and elevates preliminary data into a universal cure narrative ahead of robust evidence.

Summary

The viral claim that a “single injection causes tumors to disappear in 5 days” is misleading and misrepresents recent cancer research findings. While studies on dostarlimab and amivantamab demonstrate genuine progress for specific types of cancer, the reality differs substantially from the claim: these treatments involve multiple doses administered over weeks or months rather than a single injection, and tumor responses take considerably longer than five days to develop. These advances mark important progress in targeted cancer therapy for particular patient populations, but they do not represent the immediate, universal cure implied by the viral post.