NEW YORK (AP) — Sure things in Hollywood are beginning to look like an endangered species.

Sequels, for years the industry’s most “can’t miss” assets, are struggling at the box office this year. The downturn, which continued over the weekend with the low turnout for “Teenage Mutant Ninja Turtles: Out of the Shadows,” calls into question one of the industry’s bedrocks of bankability.

Roughly two decades ago, the sequel – once largely seen as a blatant and disrespected cash grab – threw off its stigma. Comic-book serials and long-running franchises stretched the sequel business into a new realm of round-the-clock production and box-office records.

That era is nowhere close to ending; the most popular franchises have plans in place to last the next three presidential elections. But the recent sequel slump suggests that Hollywood may have become too quick on the sequel trigger – that maybe not every profitable movie deserves a second chapter, that the world might not have been craving another “Ninja Turtles” or “Zoolander.”

No studio executive today could get away with not ordering up a sequel to a $1 billion-grossing movie like 2010’s “Alice in Wonderland.” Yet the drop was staggering for the badly reviewed “Alice Through the Looking Glass,” which has made just $51.4 million domestically in three weeks.

“It’s hard to argue with $1 billion and that’s what I think keeps studios’ finger on the greenlight: ‘Press that button. Press it, press it. We just made $1 billion. Let’s go, let’s go,'” says Jeff Bock, senior box-office analyst for Exhibitor Relations. “And at some point, that just runs into the ground. Even audiences can take only so much Vin Diesel.”

Diesel’s “Fast and Furious” franchise is one of the more astounding success stories in recent box office history. Last year’s seventh installment topped $1.5 billion worldwide; naturally, there are plans for eight, nine and 10.

In such an environment, the fast-paced greenlighting of sequels isn’t just good business, it’s like minting money. Of the top 10 films of 2016 thus far, nine are sequels, spinoffs or reboots.

And while sequels may have recently dipped, originality is cratering. Last weekend, the romance “Me Before You” performed well with $18.7 million, but the well-received Andy Samberg comedy “Popstar: Never Stop Never Stopping” flopped with just $4.7 million.

Still, “sequel underperforms” has become the steady drumbeat of 2016. “Batman v Superman: Dawn of Justice” has made $872.2 million globally, but the $250-million film has struggled to turn a profit for Warner Bros. and been roundly lambasted by critics and moviegoers alike. “X-Men: Apocalypse,” ”Neighbors 2: Sorority Rising,” ”Ride Along 2″ and “The Huntsman: Winter’s War” have all done worse than their preceding films.

Bock calls the recent sequel swoon a trend that should “cause panic” within the Hollywood studio system. It is, after all, a system currently built on the sequel business; a sequel problem for Hollywood would be like if cars went out of favor for Detroit.

“Conjuring 2” and “Now You See Me 2,” will brave any sequel-itis this week. “Finding Dory,” ”Independence Day: Resurgence,” ”Ghostbusters,” ”Star Trek Beyond” and “Jason Bourne” are all on tap this summer. Pixar’s “Finding Dory” – a sequel to 2003’s “Finding Nemo” – is widely expected to be among the season’s biggest hits, and perhaps benefits from the 13-year break since the 2013 original.

“There is something to be said for absence makes the heart grow fonder,” says Bock. “Studios need to realize that in the long term, you can kill a franchise really quickly, like the ‘Spiderman’ one, by throwing out films that are not near and dear to the hearts of audiences.”

If there’s a silver lining in the underperforming sequels, it’s that few of them have been in franchises as blue-chip as “Spider-Man,” which floundered in a too-quick reboot. It’s not altogether shocking that another “Teenage Mutant Ninja Turtles,” a Tim Burton-less “Alice” and “Zoolander 2” weren’t enticing to moviegoers; some of them are just plain bad.

Critical reaction has never been a key component of the sequel business; mediocre reviews did nothing to slow “Jurassic World” from becoming one of the highest-grossing films of all time last year. But Paul Dergarabedian, senior media analyst for comScore, believes that with social media speeding up reaction, quality is becoming essential to sequels.

“It’s a wake-up call,” says Dergarabedian. “It says to the industry just because something did well, you can’t exploit it. You have to enhance it. It has to be additive if you want to make a great sequel.”

The most glaring exception to the trend has been “Captain America: Civil War,” the highest-grossing film of the year at $1.1 billion worldwide; the Marvel train keeps chugging.

Bock, citing the planned mash-up between “21 Jump Street” and “Men in Black,” wonders if such “Avengers”-style team-up films may be the future for sequels. Could Teenage Mutant Ninja Turtles join the next “Transformers” film? It’s a chilling new frontier to ponder.

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